DDL. data defination language for creating database

Copyright © 2009, Oracle. All rights reserved.
Using DDL Statements
to Create and Manage Tables

9 - 2
Objectives
After completing this lesson, you should be able to do the
following:
• Categorize the main database objects
• Review the table structure
• List the data types that are available for columns
• Create a simple table
• Explain how constraints are created at the time of table
creation
• Describe how schema objects work

9 - 3
Object Description
Table Basic unit of storage; composed of rows
View Logically represents subsets of data from one or
more tables
Sequence Generates numeric values
Index Improves the performance of some queries
Synonym Gives alternative names to objects
Database Objects

9 - 4
 A table is a database object used to store data.
 Data in a table is organized in rows and columns.
 Each row in a table represents a unique record and each
column represents an attribute of the record.
Managing Tables
As a database developer, you
need to create and manage
tables to store data.

9 - 5
• You must have:
– The CREATE TABLE privilege
– A storage area
• In the syntax:
Schema : Is the same as the owner’s name
table : Is the name of the table
DEFAULT expr: Specifies a default value if a value is
omitted in the INSERT statement
Column : Is the name of the column
datatype : Is the column’s data type and length
CREATE TABLE [schema.]table
(column datatype [DEFAULT expr][, ...]);
CREATE TABLE Statement

9 - 6
Table names and column names:
• Must begin with a letter
• Must be 1–30 characters long
• Must contain only A–Z, a–z, 0–9, _, $, and #
• Must not duplicate the name of another object owned by
the same user
• Must not be an Oracle server–reserved word
Use descriptive names for tables and other database objects.
Naming Rules
Naming Guidelines
Note
Names are case-insensitive. For example, EMPLOYEES is treated
as the same name as eMPloyees or eMpLOYEES.

9 - 7
Data Type Description
VARCHAR2(size) Variable-length character data
CHAR(size) Fixed-length character data
NUMBER(p,s) Variable-length numeric data
DATE Date and time values
LONG Variable-length character data (up to 2 GB)
CLOB Character data (up to 4 GB)
RAW and LONG
RAW
Raw binary data
BLOB Binary data (up to 4 GB)
BFILE Binary data stored in an external file (up to 4 GB)
ROWID A base-64 number system representing the unique
address of a row in its table
Data Types

9 - 8
Datetime Data Types
You can use several datetime data types:
Data Type Description
TIMESTAMP Date with fractional seconds
INTERVAL YEAR TO
MONTH
Stored as an interval of years
and months
INTERVAL DAY TO
SECOND
Stored as an interval of days, hours, minutes,
and seconds

9 - 9
Datetime Data Types
• The TIMESTAMP data type is an extension of the DATE
data type.
• It stores the year, month, and day of the DATE data type
plus hour, minute, and second values as well as the
fractional second value.
• You can optionally specify the time zone.
TIMESTAMP[(fractional_seconds_precision)]
WITH TIME ZONE
WITH LOCAL TIME ZONE

9 - 10
Datetime Data Types
• The INTERVAL YEAR TO MONTH data type stores a
period of time using the YEAR and MONTH datetime fields:
• The INTERVAL DAY TO SECOND data type stores a
period of time in terms of days, hours, minutes, and
seconds:
INTERVAL YEAR [(year_precision)] TO MONTH
INTERVAL DAY [(day_precision)]
TO SECOND [(fractional_seconds_precision)]

9 - 13
Referencing Another User’s Tables
• Tables belonging to other users are not in the user’s schema.
• You should use the owner’s name as a prefix to those tables.
USERB
USERA
SELECT *
FROM userB.employees;
SELECT *
FROM userA.employees;

9 - 14
• Consider the following Student table.
Columns Data Type
Sno Number(5)
Sname Varchar2(12)
Course Varchar2(10)
Doj Date
Fees Number(8,2)
Creating a Table

9 - 15
• You can use the following statement to create the Student table:
The above create statement creates a table named Student where all the
columns can store null values.
Creating a Table (Contd.)
CREATE TABLE Student(
Sno Number(5),
Sname varchar2(12),
Course varchar2(10),
Doj Date,
Fees Number(8,2)
);
• Use the following command to view the structure of Student table:
DESC [RIBE] Student

9 - 16
• Specify a default value for a column during an insert.
• The default data type must match the column data type.
... JoiningDate DATE DEFAULT SYSDATE, ...
CREATE TABLE hire_dates(
id NUMBER(8),
hire_date DATE DEFAULT SYSDATE
);
CREATE TABLE succeeded.
DEFAULT Option

9 - 17
• Consider the following EmployeeLeave table.
Columns DataType Default
EmployeeID Number(5)
LeaveStartDate Date SYSDATE
LeaveEndDate Date
LeaveReason Varchar2(15)
LeaveType Char(2) CL

9 - 18
CREATE TABLE EmployeeLeave(
EmployeeID Number(5),
LeaveStartDate Date DEFAULT SYSDATE,
LeaveEndDate Date,
LeaveReason Varchar2(15)
LeaveType Char(2) DEFAULT ‘CL’
);
DESCRIBE EmployeeLeave
• Create the table.
• Confirm table creation.

9 - 19
• Create a table and insert rows by combining the
CREATE TABLE statement and the AS subquery option.
CREATE TABLE table_name
[(column, column...)]
AS subquery;
Creating a Table by Using a Subquery
• Match the number of specified columns to the number of
subquery columns.
• Define columns with column names and default values.

9 - 20
CREATE TABLE Dept30
AS
SELECT EmpNo, EmpName,
Sal*12 ANNSAL,
Hire_Date
FROM Emp
WHERE DeptNo = 30;
CREATE TABLE Succeeded.
DESCRIBE Dept30
Creating a Table by Using a Subquery

9 - 21
Use the ALTER TABLE statement to:
• Add a new column
• Modify an existing column
• Define a Default value for the new column
• Drop a column
ALTER TABLE Statement
After you create a table, you may need to change the table
structure for any of the following reasons:
 You omitted a column.
 Your column definition needs to be changed.
 You need to remove columns.

9 - 22
Adding New Columns
ALTER TABLE tablename
ADD (column datatype [DEFAULT expr] [, column datatype]...);
Modifying Columns
MODIFY (column datatype [DEFAULT expr] [, column datatype]...);
Dropping Columns
DROP (column_name); (or) DROP COLUMN column_name;

9 - 23
Adding a New Column
ALTER TABLE Student
ADD ( Address Varchar2(15) );
• If a table already contains rows when a column is added, then the
new column is initially null for all the rows.
DESC Student
• You can add or modify columns.
• You Cannot specify where the column is to appear. The new column becomes
the last column.
Guidelines
Note
Confirmation

9 - 24
ALTER TABLE Student
MODIFY( Address Varchar2(25) );
• You can increase the width or precision of a numeric / character column.
• You can decrease the width of a column only if the column contains only null
values or if the table has no rows.
• You can change the data type only if the column contains null values.
• A change to the default value of a column affects only subsequent insertions
to the table.
Modifying a Column
• You can change a column’s data type, size, and default value.
ALTER TABLE Student
MODIFY Doj Date DEFAULT SYSDATE;
Guidelines

9 - 25
Dropping a Column
ALTER TABLE Student
DROP COLUMN Address;
SELECT * FROM TAB;
• The column may or may not contain data.
• Only one column can be dropped at a time.
• The table must have at least one column remaining in it after it is altered.
• Once a column is dropped, it cannot be recovered.
Guidelines
Confirmation
ALTER TABLE Student
DROP ( Address );

9 - 26
RENAME Statement
• To change the name of a table, view, sequence, or synonym
RENAME old_name to new_name
Renaming a Table
RENAME Student to StudentInf;
Note
• You must be the owner of the object.
SELECT * FROM TAB;
Confirmation

9 - 27
TRUNCATE Statement
• Removes all rows from a table.
• Release the storage space used by that table.
TRUNCATE TABLE table_name;
Truncating a Table
TRUNCATE TABLE Student;
Note
• You cannot ROLLBACK the rows
SELECT * FROM Student;
Confirmation

9 - 28
DROP Statement
• To remove a table, view, sequence, or synonym
DROP TABLE table_name;
• The DROP TABLE statement removes the definition of an Oracle table.
Dropping a Table
DROP TABLE Student;
• When you drop a table, the database loses all the data in the table and
all the indexes associated with it.
• All data is delete from the table.
• Any views and synonyms remain but are invalid.
• Any pending transactions are committed.
Guidelines

9 - 29
Exercise
• Create StudentDetails Table.
Columns Data Type
Sno Number(5)
Sname Varchar2(12)
Addr Varchar2(15)
Mat Number(3)
Phy Number(3)
Total Number(3)
Avrg Number(3)
 Add columns
Result -- varchar2(5)
Grade -- char(1)
 Modify columns
Avrg -- number(6,2)
 Drop column Addr
 Rename the table to StudentInf
 Drop the Table
Modifications:

9 - 30
Exercise
• Create ProductDetails Table.
Columns Data Type
ProdCode Number(5)
ProdName Varchar2(12)
Price Number(10,2)
Qty Number(4)
Total Number(10,2)

9 - 31
Exercise
• Create EmployeeDetails Table.
Columns Data Type Description
Empno Number(5) Employee ID
Ename Varchar2(12) Employee Name
Job Varchar2(10) Nature of Job
Bsal Number(8,2) Basic Salary
DA Number(8,2) Dearness Allowance
TA Number(8,2) Travelling Allowance
HRA Number(8,2) House Rent Allowance
PF Number(8,2) Provident Fund
Gsal Number(8,2) Gross Salary
Nsal Number(8,2) Net Salary

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