Dbms

UNIT-I
Chapter-I : DATABASE SYSTEMS
Data: Data consists of raw facts, which the computer stores and reads. Data can consist of
letters, numbers, sounds or images etc. that have some meaning in the user environment. Data
are the raw material from which information is generated.
Information: When data has been processed to give it more meaning, it is called as
information.
Database: An organized collection of logically related data usually designed to meet the
information needs of multiple users in an organization.
Database Management System: (DBMS) is a software tool used to define, create, maintain
and provide controlled access to the database.
DBMS software stores data structures, relationship between those structures and the access
paths to those structures in a central location.
Q) How the data is organized within a database?
Ans: To help you visualize how a database stores data, think about a typical address book.
Fields: Each field contains a specific type of information such as first name, last name, phone
number, email etc…
Records: Record is a collection of related fields.
Ex: All information about one person in an address book.
Tables: A complete collection of records makes a table
Ex: Contacts table
FirstName LastName Company Address City State Pincode
Record1
Record2
Q) Why the database is important?
Ans: If you keep list of all your business customers in a database, you can
• You can sort the customers by pincode.
• Create a simple onscreen entry form that even your technically unskilled employee
can use successfully
You can manipulate data in almost anyway you want.
Files, File Systems & Problems With File System Data Management.
Manual filing system works well when the number of items stored is quite small and they are
only needed to be stored and retrieved.
A manual filing system crashes when cross referencing and processing of information in the
files is carried out.
Limitations or disadvantages of File Processing Systems.
Program data dependence: File descriptions are stored within each program that access a
given file.
In the invoicing system program access both the inventory pricing file and the customer
master file.
Page 1

Therefore this program contains a detailed description for both these files.In the below figure
both the customer master file is contained in both the order filing system and invoicing
system. Suppose it is decided to change the customer address field length in the records in
customer master file from 20 to 30 characters. For this, each related program have to be
modified.
Duplication of data or Redundancy of data: in the below figure, order filing system
contains the inventory master file, the invoicing system contains inventory pricing file.
Inventory master, inventory pricing file contains product descriptions and quantity. There is
duplication of data which requires additional storage space.
Orders Department Accounting Department
Inconsistent data: The redundancy in storing the same data multiple times leads to data
inconsistency when an update is applied to some of files but not to other.
Limited data sharing: In the file processing system, users have little opportunity to shared
data outside their applications.
Lengthy development times: Developing an application by using the file systems is very
skilled activity. The programmers has to write many programs for supporting file opening,
file closing and iterative logic for representing operations, this is very lengthy process.
Incompatible file formats: Since the structure of files is embedded in application, the
structure is dependent on application programming languages.
Ex: structure of file generated by COBOL is different from ‘C’ programming language.
The application programmer has to develop software to convert the files to some common
format for processing. This may be time consuming and expensive.
Fixed Queries: Any query or report needed by organization has to be developed by the
application programmer.
Lack of security: All users could see all data and no security and authorization subsystem.
No recovery and back up system:Data could be lost in case of hardware or software failure.
All the data is stored in disk files and accessed according to access methods (sequential,
direct etc..) provided by file system and chosen by application programmer.
Page 2
Progra
m A
Progra
m
B
Progra
m
C
Order File System
Customer
Master File
Inventory
Master File
Back Order
File
Progra
m A
Progra
m
B
Invoicing System
Inventory
Pricing File
Customer
Master File

Order
Programs
Accounting
Programs
Payroll
Programs
DBMS
Database
Customer master data
Inventory master data
Employee master data
Back order data
Q: What is a database system and What are the advantages of database systems?
Database System: Database and DBMS software together is called a database system.
Program data independence: DBMS allows certain types of changes to the structure of the
database without affecting the stored data and the existing application.
Improved data sharing: The DBMS helps create an environment in which end users have
better access to more data and better managed data.
Improved data security: The DBA uses security and authorization subsystem provided by
DBMS to create accounts and to specify account restrictions. The DBMS will enforce these
restrictions automatically.
Better Data Integration: DBMS promotes and enforces integrity rules, thus minimizing
data redundancy and maximizing data consistency.
Minimized data inconsistency: Data inconsistency is also reduced in a properly designed
database as such a database doesn’t allow different versions of same data in different places.
Ex: company’s sales department stores salesman name as ‘Bill Brown’ and the same person
name is stored as ‘William G Brown’ in company’s HR department.
Improved Data access: A query is a question or specified request issued to DBMS for data
manipulation. Example of query language is SQL
An Adhoc query is a spur of the moment question. The DBMS sends back an answer ( called
the query result set) to the application
For Ex: How many of our cutomer have balances of Rs. 3000 or more?
The DBMS gives quick answers to adhoc queries.
Improved Decision Making: Better managed data and improved data access makes it
possible to generate better quality information on which better decisions are based.
Increased end- user productivity: The availability of data and tools that transform data into
information allows end user to make quick decisions that can make the difference between
success and failure in global economy.
Page 3

Database system environment:
Database system environment is made up of five major parts. They are hardware, software,
people, procedures and data.
Hardware: Hardware refers to all of the system’s physical devices.
For ex: computers (micro computers, servers etc..), storage devices, printers, networking
devices (hubs, switches etc…) and other devices ( ATMS, ID readers etc..)
Software: Three types softwares are needed to make the database system function fully.
1. Operating system software: manages all hardware components and makes it
possible for all other software to run on the computers. Ex: UNIX, Microsoft
windows.
2. DBMS Software: manages the data within the database system.
Ex: SQL server, Oracle, DB2, My SQL
3. Application programs and utility software: are most commonly used to access data
found within the database to generate reports, tabulations and other information for
decision making. For Ex: All DBMS vendors provide GUI’s to create database
structures, control database access and monitor database operations.
4. People includes all users of database system. On the basis of their job functions, five
types of users can be identified.
1. System administrators: looks after database system general operations.
2. Database administrators (DBA) manages the DBMS and ensures that the
database is functioning properly.
3. Database Designers or Database architects design database structure. The
determination of what data are to be entered into the database and how the data are to
be organized is an important part of database designer’s job.
4. System analysts and programmers design and implement the application
programs. They design and create the data entry screens, reports and procedures
through which end users access and manipulate the database’s data.
5. End users are the people who use the application programs to run the
organisation’s daily operations. For Ex: clerks, managers, supervisors and directors.
High level end users uses the information obtained from the database to make
decisions.
5. Procedures: Procedures play an important role in a company. They enforce the
standards by which the business is conducted within the organization and with
customers. Procedures are also used to ensure that there is an organized way to
monitor and audit both the data that enter the database and the information generated
through the use of that data.
6. Data: are the raw materials from which information is generated. Data covers the
collection of facts stored in the database.
DBMS Functions:
DBMS performs several functions that guarantee the integrity and consistency of the data in
database. They are
1. Data dictionary management: The DBMS stores definitions of the data elements
and their relationships in a data dictionary. The DBMS provide data abstractions and
it removes structural and data dependency from the system.
2. Data Storage management: The DBMS creates and manages the complex structures
required for data storage, thus you need not define and program the physical data
characteristics. It also provide storage for on-screen definitions, report definitions,
data validation etc..
3. Data transformation and presentation: The DBMS must manage the data in proper
format for each country while entering dates, names etc... must not allow different
Page 4

versions of same data in different places. Ex: company’s sales department stores
salesman name as ‘Bill Brown’ and the same person name is stored as ‘William G
Brown’ in company’s HR department
4. Security Management: DBMS creates a security system that enforces user security
and data privacy. Security rules determine which users can access the database, which
data items each user can access? , which data operations (read, add, delete or modify)
the user can perform. This is important in multi user database system.
5. Multi user access control: The DBMS uses sophisticated algorithms to ensure that
multiple users can access the database at the same time.
6. Back up and recovery management: DBMS provide special utilities that allow
DBA to perform back up and restore procedures. Recovery management deals with
the recovery of database after a failure, such as bad sector in disk or power failure.
7. Data integrity management: DBMS promotes and enforces integrity rules, thus
minimizing data redundancy and maximizing data consistency.
8. Data access languages and application programming interfaces: The DBMS
provide access through a query language. A query language is a non procedural
language that lets the user specify what must be done without having to specify how it
is to be done. Example of query language is SQL
9. Database communication interface: DBMS accepts end user requests from multiple,
different network environments.
Disadvantages of DBMS
1. Increased Costs: Database system requires hardware, software and highly skilled
people. The cost of maintaining these.
2. Management Complexities: The database system hold important data that are
accessed from multiple sources, security issues may occur.
3. Frequent Updates: must perform frequent updates an d apply latest patches and
security measures to all components. These increases personnel training costs.
4. Vendor Dependence: due to heavy investment in technology and personnel training,
companies do not change database vendors. As a result, vendors donot offer pricing
point advantages to existing customers.
5. Frequent Updates / Replacement Cycles: DBMS vendors frequently upgrade their
products by adding new functionality i.e, upgrade versions of software. Some of these
versions require hardware upgrades and training to users costs money.
Page 5

UNIT-I Chapter-II
Data modeling and data models
Q: What is a data model?
Ans: Data model is blue print containing all the instructions to build a database that will meet
all the end –user requirements.
This blue print contains both text descriptions in plain, unambiguous language and clear
useful diagrams depicting the main data elements.
Q: Explain The importance of data models?
Ans:Data models are communication tool that enables interaction among the designer, the
application programmer and end user.
Data models are used to represent real world data and how the different degrees of data
abstraction enables data modeling.
Ex: a house blue print is an abstraction; you cannot live in a blue print, Similarly the data
model is an abstraction, you cannot draw the required data out of the data model. As you
cannot build a perfect house without blue print, you cannot create a good database without
creating an appropriate data model.
Q:What are Business Rules?
Ans: Business rule is a description of policy, procedure within a specific organization.
Properly written business rules are used to define entities, attributes, relationships and
constraints.
Example1: Consider 2 business rules
• A customer may generate many invoices.
• An invoice is generated by only one customer.
These business rules establish 2 entities (CUSTOMER and INVOICE) and a 1:M
relationship.
Example 2: A business rule is as follows
• A training session cannot be scheduled for <10 employees or for >30 employees
This rule establishes a constraint (not <10 employees or for >30 employees) , two entities
(EMPLOYEE and TRAINING) and a relationship between these entities.
Q: How to Discover Business Rules
Ans: The main sources of business rules are
• company managers,
• policy makers,
• department managers and
• written documentation such as a company’s procedures, standards or operation
manuals,
• direct interviews with end users.
The process of identifying and documenting business rules is essential to database design for
several reasons.
• They help standardize the company’s view of data
• They allow designer to develop relationship participation rules and constraints and to
create an accurate data model.
Q: Why not all business rules can be modeled?
Ans: For ex: No pilot can fly more than 10 hours within 24- hour period .
Such a business rule can be enforced by application software and not by database design.
Page 6

Q: Explain about hierarchical model?
Ans: Its structure is represented by an upside – down tree.
The hierarchical structure contains levels or segments.
Within the hierarchy, the top layer (also called root) is the parent of the segment directly
beneath it.
Advantages:
1. It promotes data sharing.
2. Parent child relationship promotes conceptual simplicity and data integrity.
3. Database security is provided and enforced by DBMS.
4. It is efficient with 1:M relationships.
Disadvantages:
• Complex to implement and difficult to manage as it requires knowledge of physical
data storage characteristics.
• Can implement only 1:M relationships. So it has implementation limitations.
• No standards.
• No DDL and DML language in the DBMS.
• Lacks structural independence. Changes in structure require changes in all
application programs.
• No adhoc queries
• Access paths predefined
This technology is best applied when conceptual model also resembles a tree and most data
accesses begin with the same root file.
Q: Explain about network model?
Ans: Network model allows a record to have more than one parent.
Advantages:
• It can handle M:N and multi parent relationship types.
• Data access is more flexible
• There are standards defined to implement this model.
• It includes DDL and DML commands in DBMS
Disadvantages:
• Little data independence.
• Lacks structural independence. Changes in structure require changes in all
• No adhoc queries
• Access paths predefined
Q: What is CODASYL and DBTG?
Ans: To help establish database standards, the conference on data systems languages
(CODASYL) created Database Task Group (DBTG) in late 1960s.
The final DBTG report contained specifications for 3 crucial database components.
The schema is the conceptual organization of the entire database as viewed by DBA
The subschema defines the portion of the database as seen by the application programs.
The application programs invoke the subschema required to access the appropriate database
file.
A data management language that defines the environment in which data can be managed.
Page 7

Q: Explain about The Relational Model ?
Ans: Here tables are called as “Relations”
Rows are called “Tuples” and column names as “attributes”.
Every attribute has a domain. A domain is set of permissible values that can be given to an
attribute.
A common attribute existing in any two tables creates a relationship between the tables.
It supports relationship types (1:1, 1: M or M: N)
The RDBMS manages all the physical details, while the user sees the relational database as
collection of tables. (it enables you to view data logically rather than physically.)
The RDBMS uses SQL to translate user queries into instructions for retrieving the required
data. The SQL engine executes all queries.
Advantages
• Promotes data and structural independence.
• Tabular view improves conceptual simplicity.
• Adhoc query capability is based on SQL
• RDBMS isolates end user from physical level details.
Disadvantages:
• RDBMS requires substantial hardware and software overhead.
• Conceptual simplicity gives untrained people the tools to use good system poorly.
• It may produce islands of information problems as individuals and departments can
easily develop their own applications.
Q: Explain about The Entity Relationship Model?
Ans: ER models are normally represented in an entity relationship diagram (ERD)
The ER model is based on the following components:
Entity: Entity is anything about which data are to be collected and stored
Attribute: Attributes are characteristics of entities.
Relationship:A relationship is an association between entities.
Advantages:
• Visual modeling yields conceptual simplicity.
• Visual representation makes it an effective communication tool.
• It can be integrated with dominant relational model.
Disadvantages
• There is limited constraint representation.
• There is limited relationship representation.
• There is no data manipulation language.
Q: Explain the various notations used with ERDs ?
Ans: The various notations used with ERDs are
• The chen notation favors conceptual simplicity.
• The crow’s foot notation favors implementation – oriented approach.
• The UML notation can be used for both conceptual and implementation modeling.
Q: Explain about Object Oriented model?
Ans: In this model both the data and their relationships are contained in a single structure
known as an Object.
Page 8

Object includes information about relationships between facts within the object and
relationships with other objects.
The OODM is the basis of OODBMS
The OODM is said to be semantic data model because semantic indicated meaning.
The object oriented data model is based on the following components
• An object is an abstraction of a real-world entity.
• Attributes describe the properties of an object.
• Objects that share similar characteristics are grouped in classes.
• A class is a collection of similar objects with shared structure (attributes) and
behaviour (methods) (where as entities do not have methods)
• Classes are organized in class hierarchy (which represents an upside – down tree in
which each class has only one parent)
• Inheritance is the ability of an object within class hierarchy to inherit the attributes
and methods of the classes above it.
Object oriented data models are depicted using UML diagrams.
Advantages:
• Semantic content is added
• Visual representation includes semantic content.
• Inheritance promotes data integrity.
Disadvantages:
• No widely accepted standard.
• It is a complex navigational system.
• There is a steep learning curve.
• High system overhead slows transaction.
Q) Distinguish between Logical and Physical data independence.
Logical Data Independence:
Logical data independence is the ability to modify the conceptual schema without having
alteration in external schemas or application programs. Alterations in the conceptual schema
may include addition or deletion of fresh entities, attributes or relationships and should be
possible without having alteration to existing external schemas or having to rewrite
Physical Data Independence:
Physical data independence is the ability to modify the internal schema without having
alteration to the conceptual schemas or application programs. Alteration in the internal
schema might include.
* Using new storage devices.
* Using different data structures.
* Switching from one access method to another.
* Using different file organizations or storage structures.
* Modifying indexes.
Page 9

Explain about the Conceptual, Internal and external and Physical Model
(Or)
Explain about different levels of data abstraction
(Or)
Explain about three schema architecture.
Ans:
The Conceptual Model
1. The conceptual model represents a global view of the organization’s data as viewed by all
end-users.
2. It describes all entities and their attributes, the relationships among these entities and the
constraints on these relationships.
3. The conceptual model forms the basis for the conceptual schema - a description of the
database structure.
4. The conceptual model is independent of both software (DBMS and OS) and hardware.
5. The E-R model is the most widely used to represent conceptual model
The Internal Model
Page 10

1. The internal model adapts the conceptual model to a specific DBMS (e.g., hierarchical,
network, and relational).
2. The internal model is software-dependent but hardware-independent.
3. Development of the internal model is especially important to hierarchical and network
database models.
The External Model
1. The external model is the end user’s/ applications programmer’s view (local view) of the
database .
2. It is concerned about a specific business operation.
3. It is implemented through the CREATE VIEW command in SQL.
Benefits of the external model
• Application program development is simplified because the programmer does not have to
be concerned about data not relevant to his/her application.
• Communication with the end-user is simplified.
• Identification of data required to support each business operation is simplified.
• Access control and security can be easily implemented.
Page 11

The Physical Model
• The physical model operates at the lowest level of abstraction, describing the way data
is stored on storage media such as disks or tapes.
• It requires the definition of
physical storage devices and
the access methods required to reach the data.
• The physical model is both software and hardware-dependent.
Page 12

UNIT-I
Chapter-III The Relational Database model
Explain characteristics of relational table?
1. A table is perceived as a two-dimensional structure composed of rows and columns.
2. Each table row (tuple) represents a single entity occurrence within the entity set.
3. Each table column represents an attribute, and each column has a distinct name.
4. Each row/column intersection represent a single data value.
5. All values in a column must conform to the same data format.
6. Each column has a specific range of values known as the domain of that attribute.
Example: The domain for the gender attribute consists of only two possibilities: M or F.
The domain for a company’s date of hire attribute consists of all dates (from start up date to
current date)
Attribute may share a domain.
For ex: a student address and a professor address share the same domain of all possible
addresses.
7. The order of rows and columns is immaterial to the DBMS
8. Each table must have an attribute or a combination of attributes that uniquely identifies
each row. Ex: Roll_No in the STUDENT table
What are data types support by most DBMS?
Ans: The different data types are
1. Numeric: Numeric data are data on which you can perform arithmetic operations.
2. Character: Character data or text data or string data can contain any character, symbol or
digit not intended for mathematical manipulations.
3. Date: Date attributes contain calendar dates stored in special format known as the julian
date format.
Logical: Logical data can have only a true or false (yes or no) condition.
What is data dictionary?
Ans: The data dictionary provides detailed descriptions of all tables and so contains all of
attributes names,characteristics and structure of each table in the system.
What is system catalog?
Ans: it is a detailed system data dictionary that describes all objects within the database,
including data about table names, table’s creator etc..
The system catalog is a system – created database whose tables store the user created
database characteristics and content. These tables can be queried just like user-defined table.
Explain about indexes in relational database?
Ans: An index is composed of an index key and a set of pointers. An index can be used to
retrieve data more efficiently. When you define a table’s primary key, the DBMS
automatically creates a unique index on the primary key columns.
Page 13

What is meant by functional dependence?
Ans: The attribute B is functional dependent on A
if each value in column A determines one and only one value in column B.
Ex:
What is composite key?
Ans: A key may be composed of more than one attribute. Such a multi- attribute key is known
as a composite key.
What is meant by fully functional dependency?
Ans: If attribute B is functionally dependent on a composite key A but not on any subset of
that composite key, the attribute B is fully functionally dependent on A.
Explain about various keys used in relational database model?
Key Type Definition Example
Super key An attribute (or combination of attributes)
that uniquely identifies each row in a
table.
In STUDENT table, the super key could
be any of the following:
STU_NUM
STU_NUM, STU_LNAME
Candidate
key
A minimal (irreducible) super key is a
candidate key.
A super key that does not contain a subset
of attributes that is itself a super key.
STU_NUM,STU_LNAME is a super
key, but it is not a candidate key
because STU_NUM by itself can
uniquely identifies each row in the
STUDENT table.
Primary
key
A candidate key is selected as a primary
key. It cannot contain NULL values
If employee’s PAN number has been
included as one of the attribute in the
EMPLOYEE table. EMP_NUM and
EMP_PAN are both candidate keys
because both uniquely identifies each
employee. Selection of EMP_NUM as
primary key would be designer’s
choice.
Secondary
key
An attribute or combination of attributes
used strictly for data retrieval purposes
Most of the time if I need city wise
customers list from CUSTOMER table,
I can place a secondary key on
CUS_CITY column to get a speed reply.
Foreign
key
An attribute in one table whose values must either match the primary key in another
table or be null.
Q: What is a constraint? Write short notes on integrity constraints/ rules with example?
Ans: A constraint is a restriction placed upon the data values that can be stored in a column
or columns of a table.
Integrity Constraint are of 2 types
1. Entity integrity constraint
2. Referential integrity constraint
Entity integrity : All primary key entries are unique and no part of a primary key may be null.
Referential integrity: A foreign key may have either a null entry, as long as it is not part of its
tables primary key or an entry that matches the primary key value in a table to which it is
related. (Every non- null foreign key value must reference an existing primary key value.)
Page 14

Example: Table name: AGENT
Primary key: AGENT_CODE Foreign Key: none
AGENT_CODE AGENT_FNAME AGENT_PHONE
A01 ANU 2475258
A02 RAM 2465258
Table Name: CUSTOMER
Primary Key: CUS_CODE and Foreign Key: AGENT_CODE
CUS_CODE CUS_FNAME AGENT_CODE
C01 SWATHI NULL
C02 DOLLY A01
C03 RAMA A01
Here the customer swathi is not assigned a agent yet, hence the agent code is NULL.
No entry in agent code column in customer table has invalid entry as they reference a valid
entry A01 which is anu’s agent code.
Also primary keys of both tables contain null values and has unique values.
Relational set operators or relational algebra
Relational algebra is set of basic operations used to manipulate the data in relational model.
These operations can be classified into two categories:
1. Basic set operations: These are
When two or more tables share
• the same number of columns and
• the columns have the same names and
• the columns share the same (or compatible) domains
the Two tables are said to be union-compatible.
UNION: union combines all rows from two tables, excluding duplicate rows. The two tables
must be union- compatible.
Example: R3=R1U R2
R1 R2
Page 15
Binary operations
UNION
INTERSECTION
SET DIFFERENCE
CARTESIAN PRODUCT
Relational operations
SELECT
PROJECT
JOIN
DIVISION
Fname
A1
A2
A3
A4
A7

yields
UNION
Intersect: Intersect yields only the rows that appear in both tables.
The tables must be union –compatible to yield valid results.
Page 16
Fname
A1
A2
A3
A4
Fname
A1
A7
A2
A4

Example:
R1 R2 R3=R1 n R2
yields
INTERSECT
Difference: Difference yields all rows in one table that are not found in the other table. The
tables must be union-compatible. Example:
R1 R2 R1-R2 =R3
yields
DIFFERENCE
Cartesian Product: yields all possible pairs of rows from two tables.
R3=R1X R2
R1 R2
yields
Page 17
Fname
A1
A2
A4
Fname
A1
A2
A3
A4
Fname
A1
A7
A2
A4
Fname
A3
Fname
A1
A2
A3
A4
Fname
A1
A7
A2
A4
Course Fname
C1 A1
C1 A2
C1 A3
C2 A1
C2 A2
C2 A3
Course
C1
C2
Fname
A1
A2
A3

Select: Also known as RESTRICT
Yields values for all rows found in a table that satisfy a given condition.
PRODUCT
SELECT only price < $10 yields
Project: yields all values for selected attributes. Project yield a vertical subset of a table.
PRODUCT
PROJECT Price yields
Join: A join is used to combine rows from multiple tables.
Natural Join links tables by selecting only the rows with common values in common
columns. A natural join is a result of a three-stage process.
1.a PRODUCT of the tables is created.
2. a SELECT is performed on the output to yield only the rows for which Acode =
Agent_code
and these common columns Acode, Cus_code are called as join columns.
3. a PROJECT is performed on the result to include only one join column.
Table name: CUSTOMER Table name: AGENT
STEP1: product of the above 2 tables yields
Cus_code Name Agent_code Acode Name
C01 ANU A01 A01 RAJ
C01 ANU A01 A02 TAJ
Page 18
Pcode Pdesc Price
1 Flash Light 5
2 Lamp 25
3 Battery 7
4 100W Bulb 15
Pcode Pdesc Price
1 Flash Light 5
3 Battery 7
Price
5
25
7
15
Pcode Pdesc Price
1 Flash Light 5
2 Lamp 25
3 Battery 7
4 100W Bulb 15
Cus_code Name Agent_code
C01 ANU A01
C02 RANI A02
Acode Name
A01 RAJ
A02 TAJ

C02 RANI A02 A01 RAJ
C02 RANI A02 A02 TAJ
STEP 2: SELECT rows for which Acode = Agent_code
Cus_code Name Agent_code Acode Name
C01 ANU A01 A01 RAJ
C02 RANI A02 A02 TAJ
STEP 3: PROJECT to remove Acode field from the result.
Cus_code Name Agent_code Name
C01 ANU A01 RAJ
C02 RANI A02 TAJ
The column on which the join occurs only once in new table.
Equi Join:
1. Links tables on the basis of equality condition.
2. Does not eliminate duplicate columns
Theta join : if any other comparison operator other than equality is used, the join is called
theta join.
Left outer join: yields all of the rows in CUSTOMER table, including those that do not have
a matching value in AGENT table.
Right outer join: yields all of the rows in AGENT table, including those that do not have a
matching value in CUSTOMER table.
DIVIDE: This operation uses single column table as the divisor and 2-column table as the
dividend. The tables must have a common column.
DIVIDE YIELDS
Page 19
CODE LOC
A 5
A 9
B 5
B 3
C 6
CODE
A
B
LOC
5

STUDENT
STUDENT
RollNo
STU_LNAME STU_FNAME
STU_PHONE
UNIT-II Chapter –I Entity Relationship modeling
Q: What are E-R Model Components or modules?
Ans:Three components: Entities, Attributes, and Relationships.
Entity: Entity is anything about which data are to be collected and
stored.
An entity may be concrete (a person or a book, for example) or abstract (like a holiday or a
concept).
An entity is represented by a rectangle containing entity’s name.
The entity name , a noun, is usually written in all capital letters.
Attribute:
Attributes are characteristics of entities.
For ex: STUDENT entity has the attributes
STU_FNAME,STU_PHONE etc.
Attributes are represented by ovals and are connected to the
entity rectangle with a line.
Each oval contains the name of the attribute it represents.
Attributes may share a domain.
Primary keys are underlined. (here RollNo is the primary key.)
Relationship
A relationship is an association between entities.
Relationships are described as verbs.
Relationships are represented by diamond-shaped symbols
Q: What are the different Types Of Attributes:
Ans:
1. Required and Optional Attributes:
Required attribute is an attribute that must have a value, it cannot be left empty.
Ex: STU_FNAME, STU_FNAME
Optional attribute is an attribute that does not require a value, it can be left empty.
Ex: STU_PHONE…all students may or may not have a phone at home.
2.Composite and Simple attributes:
A simple attribute cannot be subdivided.
Examples: Age, Sex, and Marital status
A composite attribute can be further subdivided to yield additional attributes.
Examples:ADDRESS into Street, City, State, Zip
PHONE NUMBER into Area code, Exchange number
3. Single-Valued and Multivalued Attributes:
A single-valued attribute can have only a single value.
Examples: A manufactured part can have only one serial number.
A multivalued attribute can have many values.
Multivalued attributes are shown by a double line connecting to the entity
Examples: i) A person may have several college degrees.
ii)A household may have several phones with different numbers
4. Derived Attribute and Stored Attribute
A derived attribute is not physically stored within the database; its value is computed from
other attributes.
It is indicated using a dotted line connecting the attribute with the entity.
Example: AGE can be derived from DOB and current date.
Page 20

What is Cardinality ?
Ans: Cardinality expresses the minimum and maximum number of entity occurrences
associated with one occurrence of the related entity.
In the ERD, cardinality is indicated by placing appropriate numbers beside the entities, using
the format (x,y).
The 1st
value represents the minimum number of associated entities,
while the 2nd
value represents the maximum number of associated entities.
These implemented by the application software or by triggers.
Q:When can you say an entity is Existence dependent/ independent?
Ans: An entity is said to be existence dependent if it can exist in the database only when it is
associated with another related entity occurrence.
Existence independence: if an entity can exist independently, then it is said to be existence
dependent.
Q:What is relationship strength? Explain about strong and weak relationships.
Ans: Relationship Strength is based on how the primary key of a related entity is defined.
They are of 2 types.
Weak (Non-identifying) relationship: a weak relationship also known as non-identifying
relationship, exists if the entity has a primary key that is not partially or totally derived from
the parent entity in the relationship
Strong relationship also known as identifying relationship, exists if the entity has a primary
key that is partially or totally derived from the parent entity in the relationship
What is Weak entity?
Ans: A weak entity is one that meets two conditions
1. The entity is existence- dependent.
2. The entity has a primary key that is partially or totally derived from the parent entity
in the relationship i.e, Strong relationship.
A weak entity id identified by using a double-walled entity rectangle.
Ex: DEPENDENT is the weak entity in the relationship EMPLOYEE has DEPENDENT.
What is meant by relationship participation?
Ans: Participation in an entity relationship is either optional or mandatory.
Optional participation means that one entity occurrence does not require a corresponding
entity occurrence in a particular relationship.
For Ex: in the “COURSE generates CLASS” relationship, there are some courses that do not
generate a class. Therefore, the CLASS entity is considered to be optional to the COURSE
entity.
Mandatory participation means that one entity occurrence require a corresponding entity
occurrence in a particular relationship
If every COURSE must generate a CLASS then the CLASS entity is considered to be
mandatory to the COURSE entity.
Types of Relationships
A relationship’s degree indicates the number of entities that participate in the relationship.
Different types of relationship degrees are :
1. Unary relationship : If an relationship is maintained within a single entity then such
relationship is called unary relationship.
Example: an employee within the EMPLOYEE entity is the manager for one or more
employees within that entity.
Page 21

when an entity has a relationship with itself then such relationship is called as recursive
relationship.
2. Binary Relationship: Binary Relationship exists when two entities are associated in a
relationship. Ex: the relationship “a PROFESSOR teaches one or more CLASSes”
What is a recursive relationship?
Ans: when an entity has a relationship with itself then such relationship is called as recursive
relationship.
What is an associative or composite or bridge entity?
Ans: When there is M:N relationship between two entities then we create a new entity called
bridge/composite entity that contains the primary keys of both the entities participating in
M:N relationship
Ex:
Explain database design challenges?
Ans:
1. Design Standards: Standards guide one in developing logical structures that reduce
data redundancies. Without design standards, it is not possible to design a proper
design or evaluate an existing design.
2. Processing Speed: high processing speed are top priority in database design as high
processing speed are necessary for many organizations
for example: a perfect design must use a 1:1 relationship to avoid nulls, while a higher
transaction –speed design might combine the two tables to avoid the use of an
additional relationship, using dummy entries to avoid nulls.
If the focus is on data-retrieval speed, one must include derived attributes in design.
3. Information requirements: a design that meets all logical requirements is an
important goal. The designer should consider end-user requirements such as
performance, security, shared access. He must also verify that all update, retrieval and
deletion options are available and also all query and reporting requirements.
Page 22

UNIT-III
Chapter-I Introduction to SQL
Q:What is SQL and What does SQL do?
SQL stands for structured query language.
SQL is non-procedural language, therefore you specify what is to be done rather than how is
it done.
American National Standards Institute (ANSI) prescribed a standard SQL.
SQL functions fits into two broad categories:
• It is a data definition language:(DDL):-SQL can create databse objects such as
tables,indexes and views.SQL can also define access rights to these database objects.
• It is a data manipulation language(DML):-SQL can be used to insert,update,delete
and retrieve data from the database
SQL is easy to learn
SQL can retrieve data from database
SQL can execute queries
SQL queries are used to answer question and also to perform actions such as adding,deleting
table rows.
Q:Explain various datatypes available in SQL?
AnsThe following table shows some common SQL datatypes
Datatype Format Comments
Numeric NUMBER(L,D) Ex: NUMBER(7,2) indicates number will be stored with two
decimal places and may be upto 7 digits long,including the
sign and decimal places.
INTEGER (OR)
INT Cannot be used if you want to store numbers that require
decimal places.
SMALLINT Limited to integer values upto six digits
DECIMAL(L,D) Greater lengths are acceptable, but smaller ones are not.
Character CHAR(L) Fixed length character data for upto 255 characters. If you
store strings that are not as long as the CHAR parameter
value,the remaining spaces are left unused
VARCHAR(L)
OR
VARCHAR2(L) Variable length character data will not leave unused spaces.
Date DATE
Stores dates in the julian date format.
Q: Explain how to create table using SQL?
Ans: The CREATE table is used to create a new table in the user database schema.
Syntax:
CREATE TABLE tablename (
Column1 datatype(column width) [constraints],
Column2 datatype(column width) [constraints],
……………
);
Page 23

Example:
CREATE TABLE VENDOR(
vno number(3) PRIMARY KEY,
vname varchar2(35) NOT NULL,
vcity varchar2(15));
If the above command is executed successfully, the message “table created “ is displayed.
The following are the rules for naming a table.
1. Table names should start with an alphabet
2. Underscores,numbers and letters are allowed but not blank spaces.
3. Maximun length of table name is 30 characters.
4. Reserved words of ORACLE cannot be used as table name.
5. Two different table should not have the same name.
6. Unique column names should be specified.
7. Proper data types and size should be specified.
Q: What are SQL constraints? Explain?
Ans: Entity integrity is enforced automatically when the primary key is specified in CREATE
TABLE command.
For Ex:
CREATE TABLE PRODUCT(
pno char(3),
pdesc varchar2(35) NOT NULL UNIQUE,
p_indate date,
qoh number(5),
price number(5),
vno number(3),
PRIMARY KEY(pno),
FOREIGN KEY(vno) REFERENCES VENDOR ON UPDATE CASCADE);
The primary key attribute contains both a NOT NULL and a UNIQUE specification.
The foreign key constraint definition ensures that
• You cannot delete a vendor from VENDOR table if atleast one PRODUCT row
references that VENDOR.
• ON UPDATE CASCADE (not supported by ORACLE) ensures that when a change is
made in VENDOR table, that change will be reflected automatically in PRODUCT
table.
Besides the primary key and foreign key constraints, the ANSI SQL standard defines the
following constraints.
• NOT NULL ensures that a column will not have null values.
• UNIQUE ensures that a column will not have duplicate values.
• DEFAULT defines a default value for a column(when no value is given).
• CHECK validates data in an attribute and sees that a specified condition exists.
Ex1: The minimum order must be atleast 10
Ex2:The date must be after APRIL 15, 2011
The CREATE TABLE command lets you define constraints in two different places.
• When you create the column definition (known as column constraint)
• When you use CONSTRAINT keyword (known as table constraint)
A column constraint applies to just one column.
A table constraint may apply to many columns.
Page 24

Q:Explain important data manipulation commands (DML) of SQL?
Ans:
INSERT: Used to enter data into a table.
Syntax:
INSERT INTO tablename VALUES (value1,value2,…..valuen)
Example:
INSERT INTO VENDOR VALUES (100,’RADHA’,’VJA’);
Observe that:
Character and date values must be entered between apostrophes(‘).
Numerical entries are not enclosed in apostrophes(‘).
Attribute entries are separated by commas.
Inserting Rows with NULL attribute
INSERT INTO product VALUES (‘P02’,’PENCIL’,’02-AUG-2011’, 25, 3, NULL);
Note that the NULL entry is accepted only because the vno attribute is optional in
PRODUCT table.
The NOT NULL declaration is not used in the CREATE TAVLE statement for these
attributes.
Inserting Rows with OPTIONAL attributes:
If the data is not available for all columns, then column list must be included following table
name.
INSERT INTO product(pno,pdesc) VALUES(‘P03’,’MOUSE’)
COPYING PARTS OF A TABLE
To create a new table based on selected column and rows of an existing table. In this
case, the new table will copy the attribute names,data characteristics and rows of
original table.
CREATE TABLE part AS
SELECT pno,pdesc,vno FROM product;
Note that no entity integrity(primary key) or referential integrity (foreign key) rules are
automatically applied to the new table.
Saving the table changes or COMMIT:
The COMMIT command permanently saves all changes such as rows added, attributes
modified and rows deleted made to any table in the database.
Syntax:
COMMIT;
Any changes made to table contents are not saved on disk until you close the database, close
the program you are using, or use the COMMIT command.
UPDATE Command:
The UPDATE command modifies an attribute value in one or more table rows.
Allows you to make data entries in an existing row’s columns.
Syntax:
UPDATE tablename
SET columnname = expression [,columnname = expression]
WHERE conditionlist;
Ex:To change the p_indate of product with pno P01 to 02-AUG-2011.
UPDATE PRODUCT
SET p_indate =’02-AUG-2011’
Page 25

WHERE pno=’P01’;
Restoring table contents or ROLLBACK:
ROLLBACK-undoes any changes since the last COMMIT command and brings the data
back to the values that existed before the changes were made.
Syntax: ROLLBACK;
Ex:
1. Create table called sales.
2. Insert 10 rows in sales table.
3. Execute the ROLLBACK command
ROLLBACK will undo only the result of INSERT and UPDATE commands.
All data definition commands(CREATE TABLE) are automatically committed to data
dictionary and cannot be rolled back.
DELETE Command
DELETE -deletes one or more rows from a table
If you do not specify a WHERE condition , all rows from table will be deleted.
REMOVAL OF SPECIFIED ROW(S):
Syntax: DELETE FROM tablename [WHERE conditionlist];
REMOVAL OF ALL ROWS:
Syntax: DELETE FROM tablename;
Viewing data in tables or SELECT
SELECT-lists the contents of a table.
Syntax:
SELECT columnlist
FROM tablename
[WHERE conditionlist];
The columnlist represents one or more attributes separated by commas.
You can use the * wildcard character to list all attributes.
Ex1: SELECT * FROM PRODUCT;
Ex2: SELECT pdesc,p_indate FROM product WHERE pno=’P01’;
Ex3:SELECT * FROM product WHERE p_indate>’01-AUG-2011’;
The SELECT statement retrieves all rows that match the specified condition.
WHERE clause adds conditional restrictions to SELECT statement.
The condition list is represented by one or more conditional expressions separated by logical
operators.
Comparison operators can be used to restrict output.
Comparison operators:
Symbol Meaning Example
= Equal to SELECT * FROM product WHERE pno=’P01’;
< Less than SELECT * FROM product WHERE price<10;
<= Less than or equal to
> Greater than SELECT * FROM product WHERE price>10;
>= Greater than or equal
to
<> or !
=
Not equal to SELECT * FROM product WHERE vno <> 100;
Using Computed Columns
Page 26

Oracle uses actual formula text as the label for the computed
column.
Ex: SELECT pno,qoh*price FROM PRODUCT;
Result:
Using Column aliases
An alias is an alternative name given to a column or table in any SQL
statement.
Ex2: SELECT pno,qoh*price AS total FROM PRODUCT;
Using Date arithmetic
SYSDATE is a special function that returns today’s date.
Ex:1 SELECT pno,p_indate,p_indate+90 AS ExpiryDate FROM product;
Ex:2 SELECT pno,p_indate,SYSDATE-90 AS CutDate FROM product
WHERE p_indate<=SYSDATE-90
The output would change based on today’s date
Arithmetic Operators:
+ Addition
- Subtraction
* Multiply SELECT qoh, price*qoh FROM
product;
/ Division
^ Raised to power(some applications uses **
instead of ^)
Rules of Precedence: Perform operations within parentheses then perform ^ then *,/ then +,-
Logical Operators:
SQL allows you to have multiple conditions in a query through the use of logical operators.
AND Both conditions must match SELECT * FROM product
WHERE price > 10 AND price < 100;
OR Either condition must match SELECT * FROM product
WHERE vno = 100 OR vno = 101
NOT Do not match a certain
condition
SELECT * FROM product
WHERE NOT(vno = 100)
Display the result when all the condition specified using the AND operator are satisfied
Display the result when Either of the condition specified using the OR operator are satisfied
NOT operator is used to find rows that do not match a certain condition. It negates the result
of conditional expression
Ex: SELECT * FROM product WHERE ( price < 50 AND p_indate > ’01-AUG-2011’) OR
vno = 100;
The rows of vno=100 are included regardless of p_indate and price of those rows.
Special Operators
BETWEEN operator:
Used to check whether an attribute value is within a range
Ex: To see list of products whose price is between $10 and $100, use the command:
Page 27
pno qoh*price
P01 PEN
P02 PENCIL
pno total
P01 PEN
P02 PENCIL

SELECT * FROM product WHERE price BETWEEN 10 AND 100;
IS NULL operator:
Used to check whether an attribute value is null.
Ex: To list all the products that do not have a vendor assigned, use the command:
SELECT * FROM product WHERE vno IS NULL;
LIKE operator:Used only with char and varchar2.
Matches a string pattern.
Used in conjuction with wildcards to find patterns within string attributes.
Ex1: To find all vendors whose name start with R
SELECT * FROM vendor WHERE vname LIKE ‘R%’;
To find all vendors whose name has ‘a’ as second letter.
Ex2: SELECT * FROM vendor WHERE vname LIKE ‘_a%’;
SQL allows you to use the percent sign (%) and underscore( _ ) wild card characters to make
matches when the entire string is not known.
Wildcard Meaning
% Matches any characters
_ Matches one characters
Matches can be made when the query entry is written exactly like table entry.
IN operator: matches any value within a VALUE list.
uses an equality operator i.e, it selects only those rows that match(are equal to) atleast
one of the values in the list
Ex:
WHERE vno IN(100 , 101);
All of the values in the list must be of same data type.
Each of the values in the value list is compared to the attribute.
IN operator is valuable when it is used in subqueries.
SELECT * FROM vendor
WHERE vno IN(SELECT vno FROM product );
Subquery (SELECT vno FROM product) will list all vendors who supply products.
IN operator will compare the values generated by subquery to vno values in VENDOR table.
EXISTS operator:checks whether subquery returns any row.
If subquery returns any row, run the main query otherwise don’t.
Ex:
SELECT * FROM vendor
WHERE (SELECT * FROM product WHERE qoh<=10);
Modifying structure of table:
ALTER Command: All changes to table structure are made using the ALTER command.
Syntax:
ALTER TABLE tablename
{ADD|MODIFY} (columnname datatype [{ADD|MODIFY} columnname datatype]);
To Change column’s datatype
Page 28

To change the vname datatype from varchar2 to char
ALTER TABLE vendor MODIFY (vname char(35));
To Change column’s data characteristics
To increase the width of vname column to 55 characters
ALTER TABLE vendor MODIFY (vname char(35));
To add a column
ALTER TABLE product ADD (pmin number(5));
If the table already has some data , we cannot add new column with NOT NULL as existing
rows will default to NULL for the new column.
TO ADD TABLE CONSTRAINTS:
Syntax: ALTER TABLE tablename ADD constraint [ADD constraint];
To add primary key:
ALTER TABLE part ADD PRIMARY KEY(part_no);
To add foreign key:
ALTER TABLE part ADD FOREIGN KEY(vno) REFERENCES vendor;
(OR)
ALTER TABLE part ADD PRIMARY KEY(part_no)
ADD FOREIGN KEY(vno) REFERENCES vendor;
To add primary and foreign key using the keyword CONSTRAINT:
ALTER TABLE part ADD CONSTRAINT pk_partno PRIMARY KEY(part_no)
ADD CONSTRAINT fk_vno FOREIGN KEY(vno) REFERENCES vendor;
TO REMOVE A COLUMN OR TABLE CONSTRAINT
Synax: ALTER TABLE tablename
DROP{ PRIMARY KEY | COLUMN columnname | CONSTRAINT constraintname};
Dropping a column: deleting a column
ALTER TABLE product DROP COLUMN pmin;
DELETING A TABLE FROM DATABASE:
A table can be deleted from the database using the DROP TABLE command.
Syntax:
DROP TABLE part;
Advanced select queries
ORDER BY clause: Orders the selected rows based on one or more attributes
• Used in the last portion of select statement
• By using this, rows can be sorted
• By default it takes ascending order
• DESC is used for sorting in descending order
• Sorting by column which is not in select list is possible.
• Sorting by column aliases
Example: To produce a list of products sorted in descending order of their prices.
SELECT pno,pdesc,p_indate,price
FROM product
Page 29

ORDER BY price DESC;
A multilevel ordered sequence is known as cascading order sequence and it can be created
easily by listing several attributes, separated by commas, after the ORDER BY clause.
SELECT * FROM employee ORDER BY e_lname,e_fname,e_initial;
DISTINCT clause: Used to eliminate duplicate rows.
Ex:How many different vendors are currently represented in the PRODUCT table?
SELECT DISTINCT vno FROM product;
Explain Aggregate functions?
Ans: Some of the aggregate functions are COUNT,MIN,MAX,AVG.
COUNT: Uses one parameter within parantheses.
COUNT(columnname)-Used to count the number of non-null values of an attribute
COUNT(*) aggregate function is used to count number of rows returned by query, including
the rows that contain nulls.
Ex1: How many rows in PRODUCT table have a price value less than or equal to $500?
SELECT COUNT(*) FROM product WHERE price<=500;
Ex:2:How many vendors referenced in the PRODUCT table have supplied products with
prices that are <+1?
SELECT COUNT(DISTINCT vno) FROM product WHERE price<=10;
MAX and MIN
Ex1: Which product has highest price?
SELECT * FROM product WHERE price = (SELECT MAX(price) FROM product);
(Here we cannot use SELECT * FROM product WHERE price = MAX(price); because The
aggregate functions can be used only in column list of a SELECT statement)
Ex2:Highest price in PRODUCT table?
SELECT MAX(price) FROM product;
Ex:3Lowest price in PRODUCT table?
SELECT MIN(price) FROM product;
Ex4: To find out the product that has the oldest date?
SELECT * FROM product WHERE price = (SELECT MIN(p_indate) FROM product);
Ex5: To find out the most recent product.
SELECT * FROM product WHERE price = (SELECT MAX(p_indate) FROM product);
SUM: Computes total sum of any specified attribute.
Ex:To find the total value of all items
SELECT SUM(qoh*price) AS TOTALVALUE
FROM product;
AVG
Ex1: To find the products whose prices exceed the average product price.
WHERE price > (SELECT AVG(price) FROM product)
ORDER BY price desc;
Explain about GROUP BY clause?
• Used to group rows on basis of certain common attribute value such as employees of
a department, products of a vendor.
Page 30

• WHERE clause can be used ,if needed.
• The only attributes that can be put in select clause are the aggregated functions and
the attributes that have been used for grouping the information.
Ex1:How many products are supplied by each vendor?
SELECT vno, COUNT(pno)
FROM product
GROUP BY vno;
Having clause:
Extension of the GROUP BY feature is the HAVING clause.
HAVING clause is applied to the output of GROUP BY operation.
Ex: how many products supplied by each vendor.List only the products whose average is
below $10
SELECT vno, COUNT(pno), AVG(price)
FROM product
GROUP BY vno
HAVING AVG(price) < 10;
Q: Explain about index in SQL
Ans:
Indexes are used to quickly access the data.
Syntax: CREATE INDEX <index name> ON <tablename>(column name);
An index can be created on one or more columns.
Based on the number of columns included in index, an index can be of 2 types.
1. Simple index 2.Composite Index.
To create Simple index:
An index created on a single column is called simple index.
Ex: CREATE INDEX p_in ON product(p_indate)
To create composite index:
An index created on a more than one column is called composite index.
Dropping indexes or deleting an index: Use the DROP INDEX command.
Ex: DROP INDEX p_in;
Q:What is database schema?
Ans:A schema is a group of database objects such as tables and indexes, that are related to
each other. Syntax: CREATE SCHEMAAUTHORIZATION {creator}
When a user is created, the DBMS automatically assigns schema to that user.
Schemas are useful to group tables by owner and enforce a first level of security by allowing
each user to see only the tables that belong to that user.
Labwork:
CREATE TABLE VENDOR(
Page 31
VENDOR
vn
o
vname vcity
10
0
RADHA VJA
10
1
ALIYA NULL
10
2
SIRI VJA
10
3
LAK GNT

vno number(3) PRIMARY KEY,
vname varchar2(35) NOT NULL,
vcity varchar2(15));
CREATE TABLE PRODUCT(
pno char(3),
pdesc varchar2(35) NOT NULL UNIQUE,
qoh number(5),
price number(5),
vno number(3),
PRIMARY KEY(pno),
FOREIGN KEY(vno) REFERENCES VENDOR);
CREATE TABLE CUSTOMER(
cno number(3) PRIMARY KEY,
cname varchar2(35) ,
city varchar2(5),
baldue number(5));
CREATE TABLE INVOICE(
invno number(3),
cno number(3),
invdate date,
PRIMARY KEY(invno),
FOREIGN KEY(cno) REFERENCES CUSTOMER);
Page 32
pno pdesc qoh price vno
P01 PEN 2 10 100
P02 CD 20 12 101
P03 PENCIL 200 3 NULL
P04 DVD 200
0
350 101
CUSTOMER
cno cname city baldue
20
1
ANU VJA 100
20
2
ASHA GNT 500
20
3
RAJ VJA
INVOICE
invno cn
o
invdate
301 20
1
20-AUG-2011
302 20
2
20-AUG-2011
303 20
3
21-AUG-2011
304 20
1
21-AUG-2011

All products sold are stored in LINE table
CREATE TABLE LINE(
invno number(3),
lineno char(3),
pno char(3),
line_units number(5),
line_price number(5),
PRIMARY KEY(invno,lineno),
FOREIGN KEY(pno) REFERENCES PRODUCT
FOREIGN KEY(invno) REFERENCES INVOICE);
CREATE TABLE EMP(
e_lname varchar2(20),
e_fname varchar2(20),
e_initial varchar2(2),
dob date,
sal number(8,2));
Page 33
LINE
invno lineno pno line_units line_price
301 L01 P01 10 10
301 L02 P02 10 12
301 L03 P03 20 3
302 L01 P01 30 10
302 L02 P02 20 12
303 L01 P01 35 10
303 L02 P02 15 12
EMP
e_lname e_fname e_initial dob Sal
REDDY SAM A 14-NOV-
1994
15000.25
NAIDU ANU S 14-OCT-1992 16234.50
JAIN NEHA K 28-NOV-
1993
15623.48
REDDY RAM T 14-SEP-1994 1623.89

Unit –III Chapter –II ADVANCED SQL
SQL data manipulation commands operate over entire table (ex: SELECT command lists all
rows from the table you specified in FROM clause) and are said to be set oriented
commands.
UNION statement:combines rows from two or more queries without including duplicate
rows.
Syntax: query UNION query
Query: SELECT cname,city FROM customer UNION SELECT cname,city FROM
customer3
Combines ouput of two or more SELECT queries. (The select statements must be union –
compatible.that is they must return the same attribute names and similar data types) without
including duplicate rows.
UNION ALL Combines ouput of two or more SELECT queries. (The select
statements must be union – compatible.that is they must return the same
attribute names and similar data types) and retains duplicate rows
SELECT cname,city FROM customer UNION ALL SELECT cname,city FROM customer3
INTERSECT statement: used to combine rows from two queries ,
returning only the rows that appear in both sets.
SELECT cname,city FROM customer INTERSECT SELECT cname,city FROM customer3
Page 34
CUSTOMER3
40
1
JAY GNT 200
40
2
RAJ VJA 300
CUSTOMER
cname city
ANU VJA
ASHA GNT
RAJ VJA
JAY GNT
CUSTOMER
20
1
ANU VJA 100
20
2
ASHA GNT 500
20
3
RAJ VJA
CUSTOMER
cname city
ANU VJA
ASHA GNT
RAJ VJA
JAY GNT
RAJ VJA
CUSTOMER
cname city
RAJ VJA

MINUS statement: combines rows from two queries and returns only
rows that appear in first set but not in the second.
SELECT cname,city FROM customer MINUS SELECT cname,city FROM customer3
SQL JOIN OPERATORS:
A join is used to combine rows from multiple tables and returns the rows with one of the
following conditions:
Join operations can be classified as inner joins and outer joins.
The inner join is traditional join in which only rows that meet a given criteria are
selected.
The join criteria can be an equality condition (also called a natural join or an equijoin) or
inequality condition( also called theta join)
Generally a join condition will be equality comparison of the P.K of one table and F.K of
related table
An outer join returns not only matching rows but also unmatched attribute values from
one table or both tables to be joined.
Join
specification
Join Type SQL
Syntax Example
Description
CROSS CROSS
JOIN
SELECT * FROM
T1,T2
SELECT *
FROM T1 CROSS
JOIN T2;
Returns the Cartesian product of T1 and
T2(old style)
Returns the Cartesian product of T1 and
T2(old style)
INNER Old-Style
JOIN
SELECT * FROM
T1,T2
WHERE
T1.C1=T2.C1;
Returns only the rows that meet the join
condition in the WHERE clause.
NATURAL
JOIN
SELECT *
FROM T1
NATURAL JOIN T2;
Returns only the rows with matching
values in the matching columns.The
matching columns must have the same
names and similar datatypes.
JOIN
USING
SELECT *
FROM T1 JOIN T2
USING(C1)
Returns only the rows with matching
values in the columns indicated in the
USING clause
JOIN ON
SELECT *
FROM T1 JOIN T2
ON T1.C1=T2.C1;
Returns only the rows that meet the join
condition in the ON clause
OUTER LEFT JOIN SELECT *
FROM T1 LEFT
OUTER JOIN T2
ON T1.C1=T2.C1;
Returns rows with matching values and
include all rows from left table(T1) with
unmatched values
RIGHT
JOIN
SELECT *
FROM T1 RIGHT
OUTER JOIN T2
ON T1.C1=T2.C1;
include all rows from right table(T2) with
unmatched values
Page 35
CUSTOMER
cno cname city
20
1
ANU VJA
20
2
ASHA GNT

FULL
JOIN
SELECT *
FROM T1 FULL
OUTER JOIN T2
ON T1.C1=T2.C1;
include all rows from both table(T1 and
T2) with unmatched values
RECURSIVE JOIN (OR) SELF JOIN:
An alias is an alternative name given to a column or table in any SQL statement.
An alias is especially useful when a table must be joined to itself in a recursive query
Ex:
SELECT E.Eno,E.Ename,M.Ename
FROM EMP E,EMP M
WHERE E.Mgr=E.Eno;
Cross Join:(also known as cartesian product) Examples:
SELECT * FROM invoice CROSS JOIN line;
The above query generates 4*7=28rows ( 4 rows in invoice table and 7 rows in line table)
Natural Join:
SELECT cno,cname,invno,invdate FROM customer NATURAL JOIN invoice;
You are not limited to two tables when performing a natural join.
It doesnot require a table qualifier for the common attribute.
SELECT invno,pno,pdesc,line_units,line_price
FROM invoice NATURAL JOIN line NATURAL JOIN product;
JOIN USING clause
It doesnot require a table qualifier for the common attribute.
SELECT invno,pno,pdesc,line_units,line_price
FROM invoice JOIN line USING(invno) JOIN product USING(pno);
JOIN ON clause
Do not require common attribute names in the joining tables.
Requires a table qualifier for the common attribute.
Lets you perform a join even when the tables do not share a common attribute name.
SELECT invoice.invno,pno,pdesc,line_units,line_price
FROM invoice JOIN line ON invoice.invno=line.invno
JOIN product ON line.pno=product.pno;
OUTER JOINS
SELECT pno,vendor.vno,vname FROM vendor LEFT JOIN product ON
vendor.vno=product.pno;
SELECT pno,vendor.vno,vname FROM vendor RIGHT JOIN product ON
SELECT pno,vendor.vno,vname FROM vendor FULL JOIN product ON
SUBQUERIES: used when it is required to process data based on other processed data
Characteristics of sub queries:
A subquery or nested query or inner query is a query inside another query.
A subquery is normally expressed inside parentheses
The output of inner query is used as input for the outer(high-level) query.
So inner query is executed first and then the outer query.
Subquery is based on the use of the SELECT statement to return one or more values to
another query. If the table into which you are inserting rows has one date attribute and one
Page 36

number attribute, the SELECT subquery should return rows in which 1st
column has date
values and 2nd
column has number values.
Inserting table rows with a select subquery or Copying parts of tables:
It add multiple rows to a table, using another table as source of the data.
CREATE TABLE PART(
part_no char(3) PRIMARY KEY,
part_desc varchar2(35),
vno number(3));
Syntax:
INSERT INTO target_tablename SELECT source_columnlist FROM source_tablename;
Example: INSERT INTO part SELECT * FROM product;
Both the tables(PART and PRODUCT) must have same attributes.The above query returns all
rows from table PRODUCT.
SELECT subquery Examples Explanation
UPDATE product
SET price=(SELECT AVG(price) FROM product )
WHERE vno=’100’………………Ex(2)
Updates the product price to
average product price for the
products provided by vendor 100.
DELETE FROM product WHERE vno IN(SELECT
vno FROM vendor WHERE vcity=’VJA’)
……………..Ex(3)
Delete the PRODUCT table rows
that are provided by vendors with
vcity=’VJA’
A subquery can return
i. One value as in Ex(2) ( the select subquery returns avg(price) which is one value).
ii. A list of values as in Ex(3) (the select subquery returns a list of vendors from ‘VJA’)
iii. A virtual table
iv. No value at all i.e, NULL . the output of the outer query might result in an error or a
null empty set.
WHERE subqueries
Ans:Ex: Find all products with a price greater than or equal to the average product price, you
write the following query.
SELECT pno,price FROM product
WHERE price>=(SELECT AVG(price) FROM product);
Note that this type of query,when used in a >,<,==,>= or <= conditional expression, requires
a subquery that returns only one single value.If the query returns more than a single value, the
DBMS will generate an error.
IN subqueries: Ans:Ex(2)
HAVING subqueries
Example:To list all products with the total quantity sold greater than the average quantity sold
SELECT pno,SUM(line_units) FROM line
GROUP BY pno HAVING SUM(line_units)>(SELECT AVG(line_units) FROM line);
MULTIROW subquery operators: ANY and ALL
1. ALL:used to do an inequality comparison(> or <) of one value to a list of values.
Example: What products have a product cost that is greater than all individual product costs
for products provided by vendor with vno 101
SELECT pno, qoh*price FROM product
WHERE qoh*price> ALL(SELECT qoh*price FROM product WHERE vno = 101);
Page 37

In the above query the ALL operator allows you to compare a single value(qoh*price) with a
list of values returned by the subquery.
2. ANY: ANY operator allows you to compare a single value with a list of values,
selecting only the
rows whose qoh*price is greater than any value of the list.
FROM subqueries
FROM clause specifies the table from which data will be drawn.
Example:To find all customers who purchased both products ‘PEN’ and ‘PENCIL’
SELECT DISTINCT cno, cname FROM customer,
( SELECT invoice.cno FROM invoice NATURAL JOIN line WHERE pdesc=’PEN’) cp1,
(SELECT invoice.cno FROM invoice NATURAL JOIN line WHERE pdesc=’PENCIL’)
cp2
WHERE customer.cno = cp1.cno AND cp1.cno=cp2.cno;
(OR)
CREATE VIEW cp1 AS
SELECT invoice.cno FROM invoice NATURAL JOIN line WHERE pdesc=’PEN’;
CREATE VIEW cp2 AS
SELECT invoice.cno FROM invoice NATURAL JOIN line WHERE pdesc=’PENCIL’;
SELECT DISTINCT cno, cname FROM customer NATURAL JOIN cp1 NATURAL JOIN
cp2;
Attribute List Subqueries or inline subquery.
The attribute list can also include a subquery expression also known as inline subquery.
The inline subquery must return one single value otherwise an error code is raised.
SELECT pno, price ,(SELECT AVG(price) FROM product) AS AVGPRICE ,
price - (SELECT AVG(price) FROM product) AS DIFF
FROM product;
The query used the full expression instead of column aliases when computing DIFF.
The column aliases cannot be used in computations in the attribute list when the alias is
defined in the same attribute list.
We can use Attribute List Subqueries to include data from other tables that are not
directly related to main table or tables in the query.
SELECT pno,SUM(line_units*line_price) AS sales,
(SELECT COUNT(*) FROM employee) AS ecount,
SUM(line_units*line_price)/ (SELECT COUNT(*) FROM employee) AS contib
FROM line
GROUP BY pno;
CORRELATED SUBQUERIES
To produce correlated subquery the DBMS does
i. It iniates the outer query
ii. For each row of the outer query result set, it executes the inner query by passing
the outer row to the inner query.( inner query references a column of the outer
subquery)
Example:To find all product sales who units sold > average units sold for that product.
SELECT invno, pno, line_units FROM line LS
WHERE LS.line_units>(SELECT AVG(line_units) FROM line LA WHERE LA.pno =
LS.pno);
Page 38

The inner query runs once using the first pno found in the outer line table and returns average
sale for that product.
CORRELATED subqueries can also be used with EXISTS special operator
Example: To know the vendor code and name for the products having qoh<10
SELECT vno, vname FROM vendor
WHERE EXISTS(SELECT * FROM product WHERE qoh<10 AND
vendor.vno=product.vno);
SQL functions: Used to generate information from data.
DUAL: is Oracle pseudo table used only for cases when a table is not really needed.
DATE/TIME FUNCTIONS
Function Examples
LAST_DAY:
returns the last day of the month based
on a date value.
Syntax:
last_day( date_value )
SELECT last_day(to_date('2003/03/15',
'yyyy/mm/dd')) FROM DUAL; would return Mar 31,
2003
SELECT last_day(to_date('2003/02/03',
'yyyy/mm/dd')) FROM DUAL; would return Feb 28,
2003
List employees born in the last seven days of a month
SELECT * FROM emp WHERE dob >=
LAST_DAY(dob)-7;
TO_CHAR function :
converts a number or date to a string.
Syntax: TO_CHAR(date_value,fmt)
fmt = format used can be
MONTH Name of month
MON:three-letter month name
MM-two digit month name
D Day of week (1-7).
DAY Name of day.
DD Day of month (1-31).
YYYY 4-digit year
YY: two digit year value
SELECT to_char(sysdate, 'yyyy/mm/dd') FROM DUAL;
would return '2003/07/09'
List all employees born in 1994.
SELECT * FROM emp WHERE
TO_CHAR(dob,’YYYY’)=’1994’;
List all employees born in the month of NOVEMBER
TO_CHAR(dob,’MM’)=’11’;
List all employees born on 14th
of a month
TO_CHAR(dob,’DD’)=’14’;
TO_DATE function:converts a string
to a date. Also used to translate a date
between formats.
Syntax: TO_DATE(char_value,fmt)
fmt = format used can be as above
SELECT to_date('2003/07/09', 'yyyy/mm/dd') FROM
DUAL;
would return a date value of July 9, 2003.
Find the age of employess as on 12-31-2012
SELECT
e_lname,TO_DATE(’12/31/2012’,’MM/DD/YYYY’)-
dob/365 AS YEARS FROM emp;
NOTE: ‘12/31/2012’ is a text string, not a date,
TO_DATE translates the text string to a valid oracle
date used in date arithmetic.
How many days are between 6/25/2011 and
10/27/2011
SELECT
TO_DATE(’2011/06/25’,’YYYY/MM/DD’)-
TO_DATE(‘OCTOBER 27,2011’,’MONTH
Page 39

,DD,YYYY’) FROM DUAL;
SYSDATE : returns todays date SELECT TO_DATE(’25-DEC-2011’,’DD-MON-
YYYY’)-SYSDATE FROM dual;
ADD_MONTHS: adds months to a
date.
Syntax:
add_months( date_value, n )
date_value is the starting date (before
the n months have been added).
n is the number of months to add to
date1.
SELECT add_months('01-Aug-03', 3) FROM DUAL;
would return '01-Nov-03'
SELECT pno,p_indate,ADD_MONTHS(p_indate,24)
FROM product
NUMERIC FUNCTIONS
Aggregate functions operate over a set of values(multiple rows) while numeric functions operate
over a single row.
Function Example
ABS
Returns absolute value of a number.
Syntax: ABS(numeric_value)
SELECT ABS(1.95),ABS(-1.93) FROM
DUAL;
Would return 1.95 1.93
ROUND function returns a number rounded
to a certain number of decimal places.
Syntax:ROUND(numeric_value,p)
p=precision
SELECT round(125.315) FROM DUAL;
would return 125
SELECT ROUND(sal) as sal1, ROUND(sal) as
sal2 FROM emp;
CEIL function returns the smallest integer
value that is greater than or equal to a
number.
Syntax: ceil( number )
SELECT ceil(-32.65) FROM DUAL;
would return -32.
SELECT ceil(32.65) FROM DUAL; would
return 33.
SELECT CEIL(sal) ,FLOOR(sal) FROM emp;
FLOOR function returns the largest integer
value that is equal to or less than a number.
Syntax: floor( number )
SELECT floor(5.9) FROM DUAL; would
return 5
SELECT floor(-5.9) FROM DUAL; would
return -6
The sqrt function returns the square root of
n.
Synatx: sqrt( n )
n is a positive number.
sqrt(9) would return 3
mod function returns the remainder of m
divided by n
mod(15, 4) would return 3
power function returns m raised to the nth
power.
Syntax : power( m, n )
m is the base. n is the exponent.
If m is negative, then n must be an integer.
power(3, 2) would return 9
Page 40

exp function returns e raised to the nth
power, where e = 2.71828183.
exp(3) would return 20.0855369231877
trunc function returns a number truncated to
a certain number of decimal places.
trunc(125.815, 0) would return 125
trunc(125.815, 1) would return 125.8
ln function returns the natural logarithm of a
number.
ln(20) would return 2.99573227355399
log function returns the logarithm of n base
m.
Syntax: log( m, n )
m must be a positive number, except 0 or 1.
n must be a positive number.
log(100, 1) would return 0
String Functions: are useful to concatenate strings of characters, printing names in upper case or
knowing the length of a given attribute.
Function Example
UPPER function converts all
letters in the specified string to
uppercase.
Syntax: UPPER(string)
upper('Tech on'); would return 'TECH ON
List all employee names in upper case.
SELECT UPPER (e_initial) || ‘.’|| UPPER (e_fname) ||
UPPER(e_lname) FROM EMP;
LOWER function converts all
letters in the specified string to
lowercase.
Syntax: LOWER(string)
List all employee names in lower case.
SELECT LOWER (e_initial) || ‘.’|| LOWER (e_fname) ||
LOWER(e_lname) FROM EMP;
SUBSTR function allows you to
extract a substring from a string.
Syntax:substr( string, p, l )
string is the source string.
p is the position for extraction.
l is optional. It is the number of
characters to extract.
substr('This is a test', 6, 2) would return 'is'
substr('This is a test', 6) would return 'is a test'
substr('This is a test', -3, 3) would return 'Net'
List first 3 characters of all employee last names..
Ex:SELECT SUBSTR(e_lname,1,3) AS prefix FROM EMP;
LENGTH function returns the
number of characters in the
specified string.
Syntax:
length( string)
length(NULL) would return NULL.
length('') would return NULL.
length('Tech on the Net') would return 15.
List all employees last names and length of their last names.
SELECT e_lname, LENGTH(e_lname) FROM EMP;
Concatenation
The || operator allows you to
concatenate data from two
different character columns and
returns a single column.
Syntax: string1 || string2
'a' || 'b' || 'c' || 'd' would return 'abcd'.
List all employee names (concatenated)
SELECT e_initial || ‘.’|| e_fname || e_lname AS NAME
FROM EMP;
CONVERSION FUNCTIONS:allows you take a value of given data type and convert it to the
equivalent value in another data type.
Functions Example
TO_CHAR : returns a
character string from a
numeric value.
Syntax:
SELECT eno, TO_CHAR(sal, ‘9,999.99’) AS PRICE FROM
EMP;
Page 41

TO_CHAR(numeric_value,
fmt)
TO_NUMBER : returns a
formatted number from a
character string.
Syntxa:TO_NUMBER
(char_value, fmt)
fmt= format used can be:
9 - displays a digit
0 – displays a leading zero
, - displays the comma
. – displays the decimal point
$ - displays the dollar sign
B – leading blank
S – leading sign
MI – trailing minus sign
SELECT TO_NUMBER(‘-123.99’,’S9999.99’),
TO_NUMBER(’99.78-’,’B999.99MI’), FROM DUAL;
DECODE: compares an
attribute or expression with a
series of values and returns
an associated value or a
default value if no match is
found
Syntax: DECODE(e,x,y,d)
e – attribute or expression
x – value with which to
compare e
y – value to return in e = x
d – default value to return if e
is not equal to x
The following example returns the sales tax for specified
cities.
Compares vcity to ‘VJA’ ;if the value matches it returns .08
Compares vcity to ‘GNT’ ;if the value matches it returns .05
If there is no match it returns 0.00( the default value)
SELECT vno, vcity,
DECODE(vcity,’VJA’,.08,’GNT’,.05,0.00) AS TAX FROM
VENDOR;
Page 42

Oracle sequences: generates a numeric value that can be assigned to any column in any
table.
Use of sequences is optional, you can enter the values manually.
Oracle sequences have a name and can be used any where a value is expected.
Sequences can be created and deleted anytime.
The table attribute to which you assigned a value based on a sequence can be edited and
modified.
Oracle sequences are
• Independent objects in the database.
• Not a data type
• Not tied to a table or column
Syntax:
CREATE SEQUENCE name [START WITH n] [INCREMENT BY n] [CACHE |
NOCACHE]
where name is the name of the sequence
n is an integer that can be positive or negative.
START WITH specifies initial sequence value( the default value is 1)
INCREMENT BY determines the value by which the sequence is incremented.
The CACHE or NOCACHE indicates whether oracle will preallocate sequence numbers in
memory. (Oracle preallocates 20 values by default)
Example: CREATE SEQUENCE CSEQ1 START WITH 204 INCREMENT BY 1
NOCACHE;
To check all the sequences you have created.
SELECT * FROM USER_SEQUENCES;
To use sequences during data entry
you must use two special pseudo columns NEXTVAL and CURRVAL.
NEXTVAL retrieves the next available value from a sequence. Each time you use
NEXTVAL , the sequence is incremented.
CURRVAL retrieves the current value of sequence.
Example
INSERT INTO CUSTOMER VALUES (CSEQ1.NEXTVAL,’RAVI’,’NELLORE’, 500);
INSERT INTO INVOICE VALUES (‘I05’ , CSEQ1.CURRVAL,’22-AUG-2011’);
You cannot use CURRVAL unless a NEXTVAL was issued previously in the same session.
NEXTVAL retrieves the next available sequence number( here 204) and signs to cno in
CUSTOMER table.
CSEQ1.CURRVAL refers to last used CSEQ1.NEXTVAL sequence number(204).
In this way the relationship between INVOICE and CUSTOMER is established.
COMMIT; statement must be issued to make the changes permanent.
You can also issue a ROLLBACk statement , in which case the rows you inserted in
INVOICE and CUSTOMER will be rolled back.( but sequence number would not) That is, if
you use sequence number again you must get 204 but you will get 205 eventhough the row
204 is deleted.
DROPPING a SEQUENCE doesnot delete the values you assigned to table attributes.
Syntax: DROP SEQUENCE CSEQ1;
Page 43

VIEWS
A view is a virtual table based on SELECT query.
The tables on which view is based are called base tables.
Syntax:
CREATE VIEW viewname AS SELECT query
Characteristics:
A relational view has several special characteristics
• We can use the view instead of table in a SQL statement.
• Views are dynamically updated when the base table is updated.
• Views provide a level of security in the database. The view can restrict users to only
specified columns and specified rows in a table.
• View may also be used as the basis for reports
Example: CREATE VIEW PROD_STATS AS SELECT vno, SUM(qoh * price) AS TotalCost
FROM PRODUCT GROUP BY vno;
To drop a view
Syntax: DROP VIEW <view name>
Example:
DROP VIEW PROD_STATS
UPDATABLE VIEWS:To use batch update routines to update master table attribute with
transaction data.
To demonstrate a batch update routine, consider two tables
NOTE:There is 1:1 relationship between two tables
To Update qoh attribute (qoh – qty as that much quantity has been sold)
1. We have to join two tables
2. update qoh for each row of ProdMaster table with matching pno values in ProdSales
table.
We use a updatable view to do that.
Updatable view is a view that can be used to update attributes in the base tables that are used
in the view.
Not all views are updatable.
The most common updatable view restrictions are as follows:
1. GROUP BY and aggregate functions cannot be used.
2. Cannot use SET operators.
3. The P.K columns of base table you want to update must have unique values in the
view. That is, the two tables must have 1:1 relationship then only the view can be
used to update a base table.
Example: CREATE VIEW QUP AS ( SELECT ProdMaster.pno, qoh, qty FROM ProdMaster,
ProdSales
WHERE ProdMaster.pno=ProdSales.pno);
Page 44
ProdMaster
pno pdesc qoh
P01 SCREWS 60
P02 NUTS 37
P03 BOLTS 50
ProdSales
pno qty
P01 7
P02 3

UPDATE QUP SET qoh=qoh-qty;
Page 45

Q: What is PSM (Persistent Stored Module)?
Ans: A Persistent Stored Module is a block of code containing standard SQL statements and
procedural extensions that is stored and executed at the DBMS server. The PSM represents
business logic that can be encapsulated, stored and shared among multiple database users. A
PSM lets an administrator assign specific access rights to a stored module to ensure that only
authorized users can use it. Oracle implements PSMs through its procedural SQL language.
(PL/SQL)
Q: What is PL/SQL? Explain?
Ans: PL/SQL is a language that makes it possible to use and store procedural code and SQL
statements within the database.
It is also used to merge SQL and traditional programming constructs, such as
• Variables,
• conditional processing (IF-THEN-ELSE),
• basic loops (FOR and WHILE loops) and
• Error trapping.
The procedural code is executed as a unit by the DBMS when it is invoked by the end user.
End users can use PL/SQL to create
• Anonymous PL/SQL blocks.
• Triggers
• Stored Procedures
• PL/SQL functions
You can write PL/SQL code block by enclosing the commands inside BEGIN and END
clause.
Ex:
BEGIN
INSERT INTO vendor VALUES (105, ‘SITA’, ‘TNL’);
END;
/
This is an example of anonymous PL/SQL block because it has not given a specific name.
The above PL/SQL block executes as soon as you press ENTER key after typing /
You will see the message “PL/SQL procedure successfully completed”
If you want a more specific message such as “new vendor added”. You must type as follows:
SQL> SET SERVEROUTPUT ON
This SQL * plus command enables the client console (SQL * plus) to receive messages from
the server side(ORACLE DBMS).To send messages from the PL/SQL block to SQL * plus
console, use the DBMS_OUTPUT.PUT_LINE function.
The standard SQL , the PL/SQL code are executed at server side, not at client side.To stop
receiving messages from sever , enter SET SERVEROUTPUT OFF.
In oracle , you can use the SQL * plus command SHOW ERRORS to help you diagnose
errors found in PL/SQL blocks.
Q: Write anonymous PL/SQL program to insert rows into VENDOR table and display
the message “New vendor added”.
Ans:
BEGIN
INSERT INTO vendor VALUES (106,’GITA’,’VJA’);
DBMS_OUTPUT.PUT_LINE(‘New vendor added’);
END;
/
Page 46

PL/SQL Basic data types
Data Type Description
CHAR character values of a fixed length
VARCHAR2 variable length character values
NUMBER numeric values
DATE Date values
%TYPE inherits the datatype from a variable that you declared previously or from an
attribute of a database table. Ex: price1 PRODUCT.price %TYPE ;
assigns price1 the same datatype as the price column in the PRODUCT table.
Q: Write anonymous PL/SQL program to display the number of products in price range
0 and 10, 11 and 60 ,61 and 110 etc..
Ans:
DECLARE
P1 NUMBER(3) := 0;
P2 NUMBER(3) := 10;
NUM NUMBER(2) := 0;
BEGIN
WHILE P2<5000 LOOP
SELECT COUNT(pno) INTO NUM FROM product WHERE price BETWEEN P1 AND P2;
DBMS_OUTPUT.PUT_LINE(‘There are ‘|| NUM|| ‘ products with price between ‘||P1|| ‘ and
‘||P2);
P1 := P2+1;
P2 := P2+50;
END LOOP;
END;
/
The PL/SQL block shown above has following characteristics.
1. Each statement inside the PL/SQL code must end with a semicolon
2. The PL/SQL block starts with the DECLARE section in which you declare the
variable names, the data types and an initial value(optional).
3. A WHILE loop is used.
4. Uses the string concatenation symbol.
5. SELECT statement uses the INTO keyword to assign output of the query to a PL/SQL
variable
The most useful feature of PL/SQL block is that they let you create code that can be named,
stored and executed either implicitly or explicitly by the DBMS.
What is Trigger ? Explain.
Ans: A trigger is a procedural sql code which is fired when a DML statements like Insert,
Delete, Update is executed on a database table.
The syntax to create a trigger in oracle is:
CREATE OR REPLACE TRIGGER trigger_name
[BEFORE / AFTER] [DELETE /INSERT/UPDATE OF column_name ] ON table_name
[FOR EACH ROW]
[DECLARE]
[variable_name data-type [:= initial_value]]
BEGIN
PL/SQL instructions;
……
Page 47

END;
A trigger definition contains the following parts:
1.The triggering timing: BEFORE or AFTER. This timing indicates at what time the
trigger should get fired. (before or after the triggering statement is completed.)
2.The triggering statement/event: The statement that causes the trigger to execute
(INSERT, UPDATE or DELETE)
The triggering level: There are two types of triggers: statement – level triggers and row –
level triggers
• Statement – level triggers: This type of trigger is executed once, before or after the
triggering statement is completed.
• Row – level triggers: requires the use of the FOR EACH ROW keywords. This type
of trigger is executed once for each row affected. ( if you update 10 rows, the trigger
executes 10 times.
2. Triggering Action: The PL/SQL code enclosed between BEGIN and END keywords.
You can use a trigger to update an attribute in a table other than the one being
modified.
CREATE OR REPLACE TRIGGER TLP
AFTER INSERT ON line
FOR EACH ROW
BEGIN
UPDATE product
SET qoh = qoh - :NEW.LINE_UNITS
WHERE product.pno = :NEW.pno;
END;
/
TLP is a row level trigger that executes after inserting a new LINE row and reduces quantity
on hand (in PRODUCT table) of recently sold product by the number of units sold.
CREATE OR REPLACE TRIGGER trigger_name =>creates a trigger with the given name
or overwrites an existing trigger with the same name.
OF column_name =>This clause is used with update triggers. This clause is used when you
want to trigger an event only when a specific column is updated
ON table_name=> the name of the table or view to which the trigger is associated.
Example of a statement level trigger that is executed after an update of the qoh, pmin
attribute for an existing row or after an insert of a new row in the product table.
CREATE or REPLACE TRIGGER TPR
AFTER INSERT OR UPDATE OF QOH,PMIN ON PRODUCT
BEGIN
UPDATE PRODUCT
SET REORDER =1
WHERE QOH <= PMIN;
END;
/
Q: When does a trigger fire?
Ans: A trigger is triggered automatically when an associated DML statement is executed.
• A trigger is invoked before or after a data row is inserted, updated or deleted.
• A trigger is associated with a database table.
• Each database table may have one or more triggers.
• A trigger is executed as part of the transaction that triggered it.
Page 48

Q: How to delete a trigger?
Ans: When you delete a table, all its trigger objects are deleted with it.
If you want to delete a trigger without deleting the table, give the following command
DROP TRIGGER triggername.
Q: Write a program to update the customer balance in the CUSTOMER table after
inserting every new LINE row.
CREATE OR REPLACE TRIGGER TLC
AFTER INSERT ON line
FOR EACH ROW
DECLARE
cus CHAR(5);
tot NUMBER := 0; --to compute total cost
BEGIN
SELECT cno INTO cus FROM invoice --1) get the customer code
WHERE invoice.invno = :NEW.line_units;
tot := :NEW.line_price * :NEW.invno; --2)compute the total of the current line
UPDATE customer SET baldue = baldue + tot WHERE cno = cus;
DBMS_OUTPUT.PUT_LINE(‘ *** Balance updated for customer : ‘ || cus);
END;
/
The trigger is a row level trigger that executes for each new LINE row inserted.
The SELECT statement returns only one attribute (cno) from INVOICE table and that
attribute returns only one value.
You use the INTO clause to assign a value from a SELECT statement to a variable (cus) used
within a trigger.
Double dashes “--“ are used to indicate comments within the PL/SQL block.
Trigger action based on conditional DML predicates
You can create a trigger that executes after an insert, an update or a delete on the PRODUCT
table and to know which one of the three statements caused the trigger to execute use the
following syntax:
IF INSERTING THEN ……END IF;
IF UPDATING THEN ……END IF;
IF DELETING THEN……END IF;
Triggers can be used to
• To enforce constraints that cannot be enforced at the DBMS design and
implementation levels.
• To facilitate enforcement of referential integrity.
• Update table values, insert records in tables and call other stored procedures.
• Triggers add functionality by automating critical actions and providing appropriate
warnings and suggestions.
• Triggers add processing power to RDBMS and to database system as a whole.
Oracle recommends triggers for
• Auditing purposes (creating audit logs)
• Automating generation of derived column values.
• Enforcement of business or security constraints.
Page 49

• Creation of replica tables for back up purposes.
Q:What are the various type of triggers?
Statement – level triggers: This type of trigger is executed once, before or after the
triggering statement is completed.
Example of a statement level trigger that is executed after an update of the qoh, pmin
attribute for an existing row or after an insert of a new row in the product table.
CREATE or REPLACE TRIGGER TPR
AFTER INSERT OR UPDATE OF QOH,PMIN ON PRODUCT
BEGIN
UPDATE PRODUCT
SET REORDER =1
WHERE QOH <= PMIN;
END;
/
Row – level triggers: requires the use of the FOR EACH ROW keywords. This type of
trigger is executed once for each row affected. ( if you update 10 rows, the trigger executes
10 times.
Example: CREATE or REPLACE TRIGGER TPR
BEFORE INSERT OR UPDATE OF QOH, PMIN ON PRODUCT
FOR EACH ROW
BEGIN
IF :NEW.QOH <= :NEW.PMIN THEN
:NEW.REORDER :=1;
ELSE
:NEW.REORDER :=0;
END IF;
END;
/
What are Stored Procedures? Explain?
A stored procedure is a named group of SQL statements that have been previously created
and stored in the server database.
Advantages:
• Stored procedures accept input parameters so that a single procedure can be
used over the network by several clients using different input data.
• Stored procedures reduce network traffic and improve performance.
• Stored procedures can be used to help ensure the integrity of the database.
• Stored procedures help reduce code duplication by means of code isolation and code
sharing, there by minimizing the chance of errors and the cost of application
development and maintenance.
• Stored procedures are useful to encapsulate shared code to represent business
transactions i.e, you need not know the name of newly added attribute and would need
to add new parameter to the procedure call.
Syntax to create procedure:
CREATE OR REPLACE PROCEDURE procedure_name [(argument [in/out] data-type,….)]
[IS / AS] [variable_name data-type [:= initial_value]]
BEGIN
PL/SQL or SQL statements;
…
END;
Page 50

Syntax to execute a stored procedure
EXEC procedure_name[(parameter_list)];
Ex: Write a stored procedure to assign an additional 5 % discount for all products when the
QOH = 2PMIN
CREATE OR REPLACE PROCEDURE prod_discount AS
BEGIN
UPDATE product
SET discount = discount + .05
WHERE qoh >= pmin * 2;
DBMS_OUTPUT.PUT_LINE(‘*** Update Finished ***’);
END;
/
1. argument specifies the parameters that are passed to the stored procedures. A stored
procedure could have zero or more arguments.
2. IN/OUT indicates whether the parameter is for input, output or both.
3. Variables can be declared between the keywords IS and BEGIN.
To make percentage increase an input variable in the above procedure---
CREATE OR REPLACE PROCEDURE prod_discount ( pd IN NUMBER)
AS BEGIN
IF ((pd <= 0) OR (pd >= 1)) THEN
DBMS_OUTPUT.PUT_LINE(‘Error value must be greater than 0 and less than 1’);
ELSE
UPDATE product
SET discount = discount + .05
WHERE qoh >= pmin * 2;
DBMS_OUTPUT.PUT_LINE(‘*** Update Finished ***’);
END IF;
END;
/
To execute the above procedure---
EXEC prod_discount(.05);
Q: write a stored procedure to add new customer.
CREATE OR REPLACE PROCEDURE cadd (w_cname IN VARCHAR2, w_city IN
VARCHAR2)
AS
BEGIN
INSERT INTO customer (cno, cname, city) values(CSEQ1.NEXTVAL, w_cname,
w_city);
DBMS_OUTPUT.PUT_LINE(‘Customer added ’);
END;
/
The procedure uses
• several parameters one for each required attribute in the CUSTOMER table.
• CSEQ1 sequence to generate a new customer code.
The parameters can be null only when the table specifications permit null for that parameter.
To execute:
EXEC cadd(‘KALA’, ‘VJA’,NULL);
Page 51

Q: Write procedures to add new invoice and line row.
Ans:
CREATE OR REPLACE PROCEDURE invadd(w_cno IN NUMBER, w_date IN DATE)
AS BEGIN
INSERT INTO invoice
VALUES(ISEQ.NEXTVAL, w_cno, w_date);
DBMS_OUTPUT.PUT_LINE(‘Invoice Added’);
END;
/
CREATE OR REPLACE PROCEDURE lineadd (ln IN CHAR, pn IN CHAR, lu IN
NUMBER)
AS
lp NUMBER := 0;
BEGIN
SELECT price INTO lp
FROM product
WHERE pno = pn ;
INSERT INTO line VALUES(ISEQ. CURRVAL, ln, pn, lu, lp);
DBMS_OUTPUT.PUT_LINE(‘Invoice Line Added’);
END;
/
Q: What is a cursor? How many types of cursors are there? How to handle cursors?
Ans:Cursor is reserved area in memory in which output of the query is stored,
like an array holding rows and columns.
There are two types of cursors: implicit and explicit.
An implicit cursor is automatically created in PL/SQL when the SQL statement returns only
one value.
An explicit cursor is created to hold the output of an SQL statement that may return two or
more rows.(but could return 0 or only one row)
To create an explicit cursor, use the following syntax inside PL/SQL DECLARE section.
CURSOR cursor_name IS select-query;
The cursor declaration section only reserves a named memory area for the cursor.
Once you declared a cursor, you can use cursor processing commands anywhere between the
BEGIN and END keywords of the PL/SQL block.
Cursor Processing Commands
Cursor Command Explanation
OPEN Executes the SQL command and populates the cursor with data
Before you can use a cursor, you need to open it Ex: OPEN
cursor_name.
FETCH To retrieve data from the cursor and copy it to the PL/SQL variables.
The syntax is : FETCH cursor_name INTO variable1 [,variable2,
…..]
CLOSE The CLOSE command closes the cursor for processing
Cursor style processing involves retrieving data from the cursor one row at a time.
The set of rows the cursor holds is called the active set.
The data set contains a current row pointer.
Therefore after opening a cursor, the current row is the first row of the cursor.
Page 52

When you fetch a row from the cursor, the data from the current row in the cursor is copied to
the pl/sql variables. After the fetch, the current row pointer moves to the next row in the set
and continues until it reaches the end of the cursor.
Cursor Attributes determine when you reached the end of the cursor data set, number of
rows in cursor etc…
Attribute Description
%ROWCOUNT Returns the number of rows fetched so far.
If the cursor is not OPEN, it returns an ERROR.
If no fetch has been done but the cursor is OPEN, it returns 0.
%FOUND Returns TRUE if the last FETCH returned a row and FALSE if not.
If no fetch has been done, it contains NULL.
%NOTFOUND Returns TRUE if the last FETCH did not return any row and FALSE if it
did.
If no fetch has been done, it contains NULL.
%ISOPEN Returns TRUE if the cursor is OPEN or FALSE if the cursor is CLOSED.
CREATE OR REPLACE PROCEDURE pce IS
p product.pno%TYPE;
desc product.pdesc%TYPE;
tot NUMBER(3);
CURSOR pc IS
SELECT pno, pdesc FROM product
WHERE qoh > (SELECT AVG(qoh) FROM product);
BEGIN
DBMS_OUTPUT.PUT_LINE(‘PRODUCTS WITH QOH > AVG(QOH)’);
OPEN pc;
LOOP
FETCH pc INTO p,desc;
EXIT WHEN pc%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(p||’ => ‘||desc);
END LOOP;
DBMS_OUTPUT.PUT_LINE(‘TOTAL PRODUCT PROCESSED ‘||pc%ROWCOUNT);
CLOSE pc;
END;
/
Page 53

Unit-III Chapter –III Database Design
Q: What is an information system?
Ans: A complete information system is composed of people, hardware, software, the
databases, application programs and procedures.
The process of creating an information system is known as system development.
Q: The system development life cycle(SDLC)
The SDLC is an iterative rather than a sequential process.
1. Planning:
The SDLC planning phase yields a general overview of the company and its objectives.
An initial assessment of the information flow-and-extent requirements must be made to
answer questions like
Should the existing system be continued?
Should the existing system be modified?
Should the existing system be replaced?
If it is decided that a new system is necessary, then it is checked whether the new system is
feasible or not. The feasibility study includes
1. Technical feasibility: Can the development of the new system be done with current
equipment, existing software technology, and available personnel? Does it require
new technology?
2. Economic feasibility: Can we afford it? Is it a million dollar solution for a thousand
dollar problem?
3. Operational feasibility: Does the company possess the human, technical and
financial resources to keep the system operational? Will there be resistance from
users?
2.Analysis:
A thorough audit of user requirements and
understanding of system’s functional areas, actual and potential problems and opportunities.
The logical design must specify the appropriate conceptual data model, inputs, processes and
expected output requirements using tools such as DFDs,ER diagrams etc..
All data transformations (processes) are described and documented using such system
analysis tools.
3.Detailed System design
The design includes all the necessary technical specifications for the screens, menus, reports
and other devices that might be used to help make the system more efficient information
generator.
4. Implementation
The hardware, DBMS software and application programs are installed and the
database design is implemented.
During the intial stages of implementation phase, the system enters into a cycle of coding,
testing and debugging until it is ready to be delivered.
The system will be in full operation by the end of this phase but will be continuously
evaluated and fine-tuned.
5. Maintenance
Maintenance includes all the activity after the installation of software that is performed to
keep the system operational.
Major forms of maintenance activities are
fixing of errors fall under corrective maintenance.
Adaptive maintenance due to changes in the business environment.
Perfective maintenance to enhance the system.
Page 54

Dbms

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Similar to Dbms

Similar to Dbms (20)

More from Lakshmi Sarvani Videla

More from Lakshmi Sarvani Videla (20)

Recently uploaded

Recently uploaded (20)

Dbms