DB2 on Mainframe

Prerequisite for DB2
The participant should be exposed to :
– IBM Mainframe Concepts
– COBOL and File Handling Concepts
– VSAM

Topics to be covered in this session
• Introduction to databases - covers their advantages
and the types of databases
• Relational database concepts - covers Properties,
Terminology, Normalization, Integrity rules, CODD’s
Relational Rules and the E-R model

Introduction to Databases
What is Data ?
‘A representation of facts or instruction in a form
suitable for communication’ - IBM Dictionary
What is a Database ?
‘Is a repository for stored data’ - C.J.Date

Introduction to Database (contd...)
What is a database system ?
An integrated and shared repository for stored data or
collection of stored operational data used by
application systems of some particular enterprise.
Or
‘Nothing more than a computer-based record keeping
system’.

Advantages of DBMS over File Mngt Sys
– Data redundancy
– Multiple views
– Shared data
– Data independence (logical/physical)
– Data dictionary
– Search versatility
– Cost effective
– Security & Control
– Recovery restart & Backup
– Concurrency

TYPES OF DATABASES (or Models)
• Hierarchical Model
• Network Model
• Relational Model
• Object-Oriented Model

Types of Databases (contd...)
HIERARCHICAL
– Top down structure resembling an upside-
down tree
– Parent child relationship
– First logical database model
– Available on most of the Mainframe computers
– Example - IMS

Types of Database (contd...)
NETWORK
– Does not distinguish between parent and child. Any
record type can be associated with any number of
arbitrary record types
– Enhanced to overcome limitations of other models
but in reality, there is minimal difference due to
frequent enhancements
– Example - IDMS

Types of Database (contd...)
RELATIONAL
– Data stored in the form of tables consists of
multiple rows and columns.
– Examples - DB2, Oracle, Sybase, Ingres etc.
OBJECT -ORIENTED MODEL
– Data attributes and methods that operate on those
attributes are encapsulated in structures called
objects

Relational Properties
– Why Relational ? - Relation is a mathematical term
for a table - Hence Relational database ‘is
perceived’ by the users as a set of tables.
– All data values are atomic.
– Entries in columns are from the same domain
– Sequence of rows (T-B) is insignificant
– Each row is unique
– Sequence of columns (L-R) is insignificant

Relational Concepts (Terminology)
– Relation : A table or File
– Tuple : Row contains an entry for each attribute
– Attributes : Columns or the characteristics that
define the entity
– Domain:. A range of values (or Pool)
– Entity : Some object about which we wish to store
information
– Null : Represents an unknown/empty value
– Atomic Value: Smallest unit of data; the individual
data value

Relational Concepts (contd...)
– Candidate key : Some attribute (or a set of
attributes) that may uniquely identify each
row(tuple) in the relation(table)
– Primary key : The candidate key that is chosen for
primary attributes to uniquely identify each row.
– Alternate key :The remaining candidate keys that
were not chosen as primary key
– Foreign key :An attribute of one relation that might
be a primary key of another relation.

Normalization (1NF - 5NF)
It is done to bring the design of database to a
standardized mode or (form)
• 1NF : All entities must have a unique identifier, or key,
that can be composed of one or more attributes. All
attributes must be atomic and non repeating.
• 2NF : Partial functional dependencies removed - all
attributes that are not a part of the key must depend
on the entire key for that entity.

Normalization (contd...)
• 3NF : Transitive dependencies removed - attributes
that are not a part of the key must not depend on any
non-key attribute.
• 4NF : Multi valued dependencies removed
• 5NF : Remaining anomalies removed

Types of Integrity
• Entity Integrity : Is a state Where no column that is
part of a primary key can have a null values.
• Referential Integrity : Is a state Where every foreign
key in the first table must either match a primary key
value in the second table or must be wholly null
• Domain Integrity : Integrity of information allowed in
column

Entity Relationship Model
• E-R model is a logical representation of data for a
business area
• Represented as entities, relationship between entities
and attributes of both relationships and entities
• E-R models are outputs of analysis phase i.e they
are conceptual data models expressed in the form of
an E-R Diagram

Example of a Relational Structure
CUSTOMER Places ORDERS
ORDERS Has PRODUCTS

The above relations can be interpreted as follows :
• Each order relates to only one customer (one-to-one)
• Many orders can contain many products (many-to-
many)
• A CUSTOMER can place any number of orders (one-to-
many)

Entity Relationship Model (contd...)
• In the above example CUSTOMER, Order & Product are
called ENTITIES.
• An Entity may transform into table(s).
• The unique identity for information stored in an
ENTITY is called a PRIMARY KEY. E.g... CUSTOMER-No
uniquely identifies each customer

A table essentially consists of
– Attributes, which define the characteristics of the
table
– Primary key, which uniquely identifies each row of
data stored in a table
– Secondary & Foreign Keys/indexes

Table Definition :
Table ‘CUSTOMER’ -
Attributes - CUST_NO, CUST_NAME,
CUST-LOCATION, CUST_ID, ORDER_NO...
Primary Key - CUSTOMER_NO
Secondary Key - CUST_ID
Foreign-Key - ORDER_NO

• The Relationships transform into Foreign Keys. For
e.g.. CUSTOMER is related to Orders through
‘ORDER_NO’ which is the Foreign-key in CUSTOMER
and Primary key in Order. So basically the relationship
‘Places’ is through the ORDER_NO.
• As per the relational integrity the Primary-Key,
ORDER_NO, for the table ‘Orders’ can never be Null,
while it can be so in the table ‘CUSTOMER’.

• Tables exist in Tablespaces. A tablespace can contain
one or more tables
• Apart from the Primary Key, a table can have many
secondary keys/indexes, which exist in Indexspaces.
• These tablespaces and indexspaces together exist in a
Database

• To do transformations as described above we need a
tool that will provide a way of creating the tables,
manipulate the data present in these, create
relationships, indexes, tablespace, indexspace and so
on. DB2 provides SQL which performs these functions.
The next part briefly deals with SQL and its functions.
A detailed explanation will be taken up later.

• SQL - all data object manipulation, creation and use,
involve SQL’s.
• DB2 objects - Database, Tablespaces & Indexspaces -
creation & use, and other terminology's associated
with databases.
• DDL - Data Definition Language

An introduction to SQL
SQL or Structured Query Language is
– A Powerful language that performs the functions of
data manipulation(DML), data definition(DDL) and
data control or data authorization(DAL/DCL).
– A Non procedural language - the capability to act on
a set of data and the lack of need to know how to
retrieve it. An SQL can perform the functions of
more than a procedure.
– The De Facto Standard query language for RDBMS
– Very flexible

Introduction to SQL (contd...)
SQL - Features :-
– Unlike COBOL or 4GL’s, SQL is coded without data-
navigational instructions. The optimal access paths
are determined by the DBMS. This is advantageous
because the database knows better how it has
stored data than the user.
– What you want and not how to get it
– Set level processing & multiple row processing

SQL - Types (based on the functionality)
• Data Definition Language (DDL)
- Create, Alter and Drop
• Data Manipulation Language (DML)
- Select, Insert, Update and Delete
• Data Control Language (DCL)
- Grant and Revoke

SQL - Types (Others)
• Static or Dynamic SQL
• Embedded or Stand-alone SQL

The following are the Operations that can be performed by
a SQL on the database tables:
• Select
• Project
• Union
• Intersection
• Difference
• Join
• Divide

Topics dealt with, in DB2 objects
• Stogroup, Databases, Tablespaces (types, creation and
modification)
• Indexspaces (creation and modification)
• Some more terms associated with tablespaces

DB2 Objects
• The DB2 Object Hierarchy

Stogroup
• It is a collection of direct access volumes, all of the
same device type
• The option is defined as a part of tablespace definition
• When a given space needs to be extended, storage is
acquired from the appropriate stogroup

Database
• A collection of logically related objects - like
Tablespaces, Indexspaces, Tables etc.
• Not a physical kind of object - may occupy more
than one disk space
• A STOGROUP & BUFFERPOOL (is buffer area used
to maintain recently accessed table and index
pages) must be defined for each database.
• Stogroup and user-defined VSAM are the two
storage allocations for a DB2 dataset definition.

Database (contd...)
• In a given database, all the spaces need not have the
same stogroup
• These are, in a sense, the most physical of various
storage objects in DB2
• More than one volume can be defined in a stogroup.
DB2 keeps track of which volume was defined first &
uses that volume.

Tablespaces
• Logical address space on secondary storage to hold
one or more tables
• A ‘SPACE’ is basically an extendable collection of pages
with each page of size 4K or 32K bytes.
• It is the storage unit for for recovery and reorganizing
purpose
• Three Type of Tablespaces - Simple, Partitioned &
Segmented

Simple Tablespace
• Can contain more than one stored table
• Depending on application, storing more than one Table
might enable faster retrieval for joins using these
tables
• Usually only one is preferred. This is because a single
page can contain rows from all tables defined in the
database.
• LOAD with replace option deletes all data

Segmented Tablespaces
• Can contain more than one stored table, but in a
segmented space
• A ‘Segment’ consists of a logically contiguous set of
‘n’ pages.
• Segsize parameter decides the allocation size for the
tablespace
• No segment is allowed to contain records for more
than one table
• Sequential access to a particular table is more efficient

Segmented Tablespaces (contd...)
• Mass Delete is much more efficient than in any other
Tablespace
• Reorganizing the tablespace will restore every table to
its clustered order
• Lock Table on table locks only the table, not the entire
tablespace
• If a table is dropped, the space for that table can be
reclaimed with minimum reorg

Partitioned Tablespaces
• Primarily used for Very large tables
• Only one table in a partitioned TS; 1 to 64
partitions/TS
• Numpart parameter specifies the no. of partitions
• It is partitioned in accordance with value ranges for
single or a combination of columns. Hence these
column(s) cannot be updated
• Individual partitions can be independently recovered
and reorganized
• Different partitions can be stored on different storage
groups for efficient access.

Tablespace parameters to be specified for TS
creation
• LOCKSIZE - indicates the type of locking DB2 performs
for the given TS
– Page
– Table
– Tablespace
– ANY - DB2 decides the starting page

Tablespace parameters (contd...)
• USING - method of storage allocations - Stogroup or
VCAT
• PCTFREE - % of space available for future inserts
• FREEPAGE - no of pages after which an empty page is
available
• BUFFERPOOL - BP1, BP2 & BP32K
• CLOSE - Yes/No - whether the underlying VSAM
datasets be closed each time the table is used. Max no
of datasets that can be open in DB2 at a time is 10,000

Tablespace parameters (contd...)
• ERASE - Yes/No - whether physical DASD Where the
TS reside to be written with binary zeros when the TS
is dropped
• NUMPARTS - For Partitioned Tablespaces
• SEGSIZE - For Segmented Tablespaces

VCAT Option
• User Defined VSAM datasets have to be defined
explicitly by the AMS utility IDCAMS
• Two types of VSAM datasets are used -ESDS & LDS.
Linear Data set is more efficiently used by DB2
• VSAM datasets defined here are different from the
plain VSAM datasets - can access them only through
VSAM Media Manager

Data Definition Language
CREATE
This statement is used to create objects
Syntax : For Creating a Table
CREATE TABLE <tabname> (Col Definitions)
PRIMARY KEY(Columns) / FOREIGN KEY
UNIQUE (Colname) (referential constraint)
[LIKE Table name / View name]
[IN Database Tablespace Name ]

Data Definition Language (contd...)
• Foreign Key references dbname.table on ‘relation
condition for delete’
• Table1 references table2(target) - Table2’s Primary key
is the foreign key defined in Table1
• The Conditions that can be used are CASCADE,
RESTRICT & SET NULL (referential constraint for the
foreign key definition)
• Inserting (or updating ) rows in the target is allowed
only if there are no rows in the referencing table

ALTER
This statement is used for altering all DB2 objects
Syntax : For altering a Table
ALTER TABLE <Tablename>
ADD Column Data-type [ not null with default]
• Alter allows primary & Foreign key specifications to be
changed
• It does not support changes to width or data type of a
column or dropping a column

DROP
This statement is used for dropping all DB2 objects
Syntax : For dropping a table
DROP TABLE <Tablename>

Some general rules for RI & Table Parameters
• Avoid nulls in columns participating in
Arithmetic logic or comparisons
• Primary key cols cannot be nulls
• Limit referential structures to no more than
three levels in a direction
• Use DB2’s inherent features rather than program
coded RI’s.

• More SQL - Insight into the DML statement Select
• Simple Queries
• Functions
• Complex Queries
• Other DML statements Insert, Update and Delete
• Dynamic SQL Vs Static SQL
• More on DB2 Objects (Indexes, Views, Alias etc...)

SQL - Selection & Projection
• Select retrieves a specific number of rows from a table
• Projection operation retrieves a specified subset of
columns(but all rows) from the table
E.g.. : SELECT CUST_NO, CUST_NAME
FROM CUSTOMER;
• The WHERE clause defines the Predicates for the SQL
operation.
• The above WHERE clause can have multiple
conditions using AND & OR .

Other Clauses
Many other clauses can be used in conjunction with
the WHERE clause to code the required predicate,
some are :-
– Between / Not Between
– In / Not In
– Like / Not Like
– IS NULL / IS NOT NULL

SELECT using a range :
Between Clause
E.g. SELECT CUST_NO, CUST_NAME, CUST_ADDR FROM
CUSTOMER
WHERE CUST_NO BETWEEN 1000 AND 2000;
In Clause
E.g. SELECT CUST_NO, CUST_NAME, CUST_ADDR
FROM CUSTOMER
WHERE CUST_NO IN(1000, 1001,1002);

Select clause (contd...)
Like Clause
FROM CUSTOMER
WHERE CUST_ID like/not like ‘425%’
Note :- ‘_’ for a single char ; ‘%’ for a string of chars
Escape ‘’ - escape char; if precedes ‘_’ or ‘%’ overrides
their meaning

Select clause (contd...)
NULL Clause : To check null the syntax is ‘IS NULL’
E.g. SELECT CUST_NO, CUST_NAME, ORDER_NO
WHERE ORDER_NO IS NULL;
However if there are null values for ORDER_NO, then
these are always evaluated as a ‘Not True’ condition in
a Query.

Order by and Group by clauses :
• Order by sorts retrieved data in the specified order;
uses the WHERE clause
• Group by operator causes the table represented by the
FROM clause to be rearranged into groups, such that
within one group all rows have the same value for the
Group by column (not physically in the database). The
Select clause is applied to the grouped data and not to
the original table.
Here ‘HAVING’ is used to eliminate groups, just like
WHERE is used for rows.

Order by and Group by clauses (contd...)
E.g. SELECT ORDER_NO, SUM(NO_PRODUCTS)
FROM ORDER
GROUP BY ORDER_NO
HAVING AVG(NO_PRODUCTS) < 10
ORDER BY ORDER_NO ;

Functions
Types are two :
– Column Function
– Scalar Function

Column Functions
• Compute from a group of rows aggregate value for a
specified column(s)
• AVG, COUNT, MAX, MIN, SUM

Scalar Functions
• Are applied to a column or expression and operate on
a single value.
• CHAR, DATE, DAY(S), DECIMAL, DIGITS, FLOAT, HEX,
HOUR, INTEGER, LENGTH, MICROSECOND, MINUTE,
MONTH, SECOND, SUBSTR, TIME, TIMESTAMP, VALUE,
VARGRAPHIC, YEAR

Complex SQL’s
• One terms a SQL to be complex when data that is
to be retrieved comes from more than one table
• SQL provides two ways of coding a complex SQL
– Subqueries and
– Joins

Subqueries
• Nested Select statements
• Specified using the IN(or NOT IN) predicate, equality or
non-equality predicate(‘=‘ or ‘<>‘) and comparative
operator(<, <=, >, >=)
• When using the equality, non-equality or comparative
operators, the inner query should return only a single
value

Subqueries (contd...)
E.g. SELECT CUST_NO, CUST_NAME
FROM CUSTOMER
WHERE ORDER_NO IN
(SELECT ORDER_NO FROM ORDER
WHERE NO_PRODUCTS <5);
E.g. SELECT CUST_NO, CUST_ADDR
FROM CUSTOMER
WHERE ORDER_NO =
WHERE NO_PRODUCTS = 5);

Subqueries (contd...)
• The nested loop statements gives the user the
flexibility for querying multiple tables
• A specialized form is Correlated Subquery - the nested
select statement refers back to the columns in
previous select statements
• It works on Top-Bottom-Top fashion
• Non-correlated Subquery works in Bottom-to-Top
fashion

Correlated Subquery
E.g. SELECT A.CUST_NAME A.CUST_ADDR
FROM CUSTOMER A
WHERE A.ORDER_NO IN
(SELECT ORDER_NO
FROM CUSTOMER B
WHERE A.CUST_ID = B.CUST_ID)
ORDER BY A.CUST_ID, A.CUST_NO ;

Corelated Subquery using EXISTS clause :
E.g. SELECT CUST_NO, CUST_NAME
FROM CUSTOMER A
WHERE EXISTS
(SELECT * FROM ORDER B
WHERE B.ORDER_NO = A.ORDER_NO
AND B.ORDER_NO = 5);

Multiple levels of Subquery
FROM CUSTOMER
WHERE ORDER_NO IN
WHERE PROD_ID IN
(SELECT PROD_ID
FROM PRODUCTS
WHERE PROD_NAME = ‘NUTS’));

Joins
OUTER JOIN : For one or more tables being joined, both
matching and non-matching rows are returned.
Duplicate columns may be eliminated
The non-matching columns will have nulls in them.
INNER JOIN: Here there is a possibility one or more of
the rows from either or both tables being joined will
not be included in the table that results from the join
operation

Other DML Statement’s
INSERT
E.g..: INSERT INTO Tablename(column1,
column2, column3 ,......)
VALUES( value1, value2, value3 ,........)
If any column is omitted in an INSERT statement and that
column is NOT NULL, then INSERT fails; if null it is set
to null

DML statements (contd...)
• If the column is defined as NOT NULL BY DEFAULT, it is
set to that default value
• Omitting the list of columns is equivalent to specifying
all values
• SELECT - INSERT
E.g. INSERT INTO TEMP (A#, B)
SELECT A#, SUM(B)
FROM TEMP1 GROUP BY A# ;

UPDATE
E.g.. UPDATE tablename
SET Columnname(s) = scalar expression
WHERE [ condition ]
• Single or Multiple row updates
• Update with a Subquery

DELETE
E.g. DELETE FROM Tablename
WHERE [condition ];
• Single or multiple row delete or deletion of all rows

Static SQL
• Hard-coded into an application program
• cannot be modified during the program’s execution
except for changes to the values assigned to the host
variables
• Cursors are used to access set-level data (i.e when a
SQL SELECT returns more than 1 row)
• The general form is EXEC SQL
[SQL statements]
END-EXEC.

Dynamic SQL
• Statements can change throughout the program’s
execution
• When the SQL is bound, the application plan or
package that is created does not contain the same
information as that for a static SQL program
• The access paths cannot be determined before
execution

Indexes
What is an Index ?
‘An index is an ordered set of pointers to rows of a
base table’.
Or
‘An Index is a balanced B-tree structure that orders
the values of columns in a table’
Why an Index ?
‘One can access data directly and more efficiently’

Indexes (contd...)
• Each index is based on the values of data in one or
more columns. An index is an object that is separate
from the data in the table.
• When you define an index using the CREATE INDEX
statement, DB2 builds this structure and maintains it
automatically.
• Indexes can be used by DB2 to improve performance
and ensure uniqueness.
• In most cases, access to data is faster with an index.
• A table with a unique index cannot have rows with
identical keys.

Indexes (contd...)
Syntax : For creation of an Index
CREATE INDEX <indexname> ON <tabname>
(colname asc/desc)

Index Parameters for Creation
• CLUSTER
• USING STOGROUP/VCAT (the corresponding name)
• FREEPAGE
• PCTFREE
• PRIQTY / SECQTY
• BUFFERPOOL
• CLOSE - Yes/No
• ERASE Yes/No

Index Guidelines - What to do ?
1. Consider indexing on columns used in UNION,
DISTINCT, GROUP BY, ORDER BY & WHERE clauses.
2. Limit the indexing of frequently updated columns
3. Create explicitly, a clustering index
4. Create a unique index on the primary key and
indexes on foreign keys

Index Guidelines (contd...)
5. Overloading of index when row length of a table to
be accessed is short
6. Atleast one index must be defined for a table with
more than 100 pages
7. Use Multicolumn index rather than a multi-index
(appln dependent); however the latter requires more
DASD .

8. Create indexes before loading the table.
9. Clustering reduces I/O; DB2 optimizer usually tries
to use an index on clustered column before using the
other indexes.
10. Specify Indexspace freespace the same as
tablespace freespace

11. Use the DEFER option while creating the index.
RECOVER INDEX utility can then be used to populate
the index. Recover utility populates index entries
faster.
12. Use different STOGROUP’s for Tablespaces &
indexspaces
13. Create Critical indexes in a different bufferpool than
the tablespaces.

Index Guidelines - What Not to do ?
1. Avoid indexing on Variable columns
2. Limit the number of indexes on partitioned TS
3. Avoid indexes if
– the table is very small (< 10 pages)
– it has heavy inserts and deletes and is relatively
small (< 20 pages)
– it is accessed with a scan.
4. Avoid defining redundant indexes

Other DB2 Objects
VIEWS
• It is a logical derivation of a table from other
table/tables. A View does not exist in its own right.
• They provide a certain amount if logical independence
• They allow the same data to be seen by different users
in different ways
• In DB2 a view that is to accept a update must be
derived from a single base table

DB2 Objects (contd...)
Aliases
• Mean ‘another name’ for the table.
• Aliases are used basically for accessing remote tables
(in distributed data processing), which add a location
prefix to their names.
• Using aliases creates a shorter name.
Synonym
• Also means another name for the table, but is private
to the user who created it.

DB2 Objects (contd...)
Syntax:
CREATE VIEW <Viewname> (<columns>)
AS Subquery (Subquery - SELECT FROM
other Table(s))
CREATE ALIAS <Aliasname> FOR <Tablename>
CREATE SYNONYM <Synonymname> FOR <Tablename>

SQL Guidelines
- Refer handout
- Mullins, chapter 2

Topic to be covered in this session
• Application programming using DB2
• Steps to write a DB2 application
• Cursors
• QMF and SPUFI
• Some Hints

Application programming using DB2
Application environments supporting DB2 :
– IMS(Batch/Online), CICS, TSO(Batch/Online)
– CAF - Call Attach Facility
– All DB2 application types can execute concurrently
– Host Language support - COBOL, PL/1, C, Fortran or
Assembly lang

Steps involved in creating a DB2 application
Coding the application
– using Embedded SQL
– using Host variables (DCLGEN)
– using SQLCA
– pre-compile the program
– compile & link edit the program
– bind
Note : Cursors can also be used

Embedded SQL statements
• It is like the file I/O
• Normally the embedded SQL statements contain the
host variables coded with the INTO clause of the
SELECT statement.
• They are delimited with EXEC SQL ...... END EXEC.
• E.g.EXEC SQL
SELECT Empno, Empname
INTO :H-empno, :H-empname
FROM EMPLOYEE
WHERE empno = 1001
END EXEC.

Host Variables
• These are variables(or rather area of storage) defined
in the host language to use the predicates of a DB2
table. These are referenced in the SQL statement.
• A means of moving data from and to DB2 tables
• DCLGEN produces host variables, the same as the
columns of the table

Host Variables (contd...)
Host variables can be used
• In WHERE Clause of Select, Insert, Update & Delete
• ‘INTO’ Clause of Select & Fetch statements
• As input of ‘SET’ Clause of Update Statements
• As Input for the ‘VALUES’ Clause of Insert statements
• As Literals in Select list of a Select Statement

Host Variables (contd...)
E.g. SELECT Cust_No, Cust_name, Cust_addr
INTO :H-CUST-NO, :H-CUST-NAME,
:H-CUST-ADDR
FROM CUSTOMER
WHERE CUST_NO = :H-CUST-NO;

DCLGEN
• Issued for a single table
• Prepares the structure of the table in a COBOL
copybook
• The copybook contains a ‘SQL DECLARE TABLE’
statement along with a working storage host variable
definition for the table

SQLCA
• An SQLCA is a structure or collection of variables
that is updated after each SQL statement
executes.
• An application program that contains executable
SQL statements must provide exactly one SQLCA.

SQLCA (contd...)
Structure of the SQLCA (for COBOL)
01 SQLCA.
05 SQLCAID PIC X(8).
05 SQLCABC PIC S9(9) COMP
05 SQLCODE PIC S9(9) COMP
05 SQLERRM.
:
05 SQLWARN.
10 SQLWARN0 PIC X(1).
:
10 SQLWARNA PIC X(1).
10 SQLSTATE PIC X(5).

Cursors
• Used when a large number of rows are to be Selected
• Can be likened to a pointer
• Can be used for modifying data using ‘FOR UPDATE OF’
clause

Cursors (contd...)
The four (4) Cursor control statements are -
• Declare : name assigned for a particular SQL
statement
• Open : readies the cursor for row retrieval; sometimes
builds the result table. However it does not assign
values to the host variables
• Fetch : returns data from the results table one row at a
time and assigns the value to specified host variables
• Close : releases all resources used by the cursor

Cursors (contd...)
DECLARE
E.g. - For the Declare statement
EXEC SQL
DECLARE EMPCUR CURSOR FOR
SELECT Empno, Empname,Dept, Job
FROM EMP
WHERE Dept = 'D11'
FOR UPDATE OF Job
END-EXEC.

Cursors (contd...)
OPEN
E.g. - For the Open statement
EXEC SQL
OPEN EMPCUR
END-EXEC.

Cursors (contd...)
FETCH
E.g. - For the Fetch statement
EXEC SQL
FETCH EMPCUR
INTO :Empno, :Empname, :Dept, :Job
END-EXEC.

Cursors (contd...)
CLOSE
E.g. - For the Close statement
EXEC SQL
CLOSE EMPCUR
END EXEC.

Cursors (contd...)
WHENEVER
E.g. - For the Whenever Clause
EXEC SQL
WHENEVER NOT FOUND
Go To Close-EMPCUR
END EXEC.
Note :- Not recommended for use in application programs

Cursors (contd...)
UPDATE
E.g. - For the Update statement using cursors
EXEC SQL
UPDATE EMP
Set Job = :New-job
WHERE current of EMPCUR
END EXEC.

Cursors (contd...)
DELETE
E.g. - For the Delete statement using cursors
EXEC SQL
DELETE FROM EMP
WHERE current of EMPCUR
END EXEC.

Application development guidelines
• Code modular DB2 programs and make them as small
as possible
• Use unqualified SQL statements; this enables
movement from one environment to another(test to
production)
• Never use ‘Select *’ in an embedded SQL program;
• Use joins rather than subqueries

Application development guidelines (contd...)
• Use WHERE clause and filter out data
• Use cursors when fetching multiple rows, though they
add overheads
• Use FOR UPDATE OF clause for UPDATE or DELETE with
cursor - this ensures data integrity.
• Use Inserts minimally ; use LOAD utility instead of
INSERT, if the inserts are not application dependent

QMF - Query Management Facility
• It is an MVS- and VM- based query tool
• allows end users to enter SQL queries to produce a
variety of reports and graphs as a result of this query
• QMF queries can be formulated in several ways : by
direct SQL statements, by means of relational
prompted query interface or by query-by-example
(QBE). QBE is similar to SQL in some ways but more
user friendly

SPUFI - SQL Processing Using File Input
• Supports the online execution of SQL statements from
a TSO terminal
• Used for developers to check SQL statements or view
table details
• SPUFI menu contains the input file in which the SQL
statements are coded, option for default settings and
editing and the output file.

Topic to be covered in this session
• Program Preparation
• Precompile, Compile, Linkedit and Bind
• Plan & Packages

Precompile
• Searches all the SQL statements and DB2 related
INCLUDE members and comments out every SQL
statement in the program
• The SQL statements are replaced by a CALL to the DB2
runtime interface module, along with parameters.
• All SQL statements are extracted and put in a Database
Request Module (DBRM)

Precompile (contd...)
• Places a timestamp in the modified source and the
DBRM so that these are tied. If there is a mismatch in
this a runtime error of ‘-818‘, timestamp mismatch
occurs
• All DB2 related INCLUDE statements must be placed
between EXEC SQL & END EXEC keywords for the
precompiler to recognize them

Compile & Link
• Modified precompiler COBOL output is compiled
• Compiled source is link edited to an executable load
module
• Appropriate DB2 host language interface module
should also be included in the link edit step(i.e DSNELI)

Bind
• A type of compiler for SQL statements
• It reads the SQL statements from the DBRM and
produces a mechanism to access data (in an efficient
manner) as directed by the SQL statements being
bound
• Checks syntax, checks for correctness of table &
column definitions against the catalog information &
performs authorization validation

Bind Types
• BIND PLAN : accepts as input one or more DBRMs and
outputs an application plan containing executable logic
representing optimized access paths to DB2 data.
• BIND PACKAGE : accepts as input a single DBRM and
produces a single package containing the optimized
access path. The PLAN in this case contains a reference
to the physical location of the package(s).

What is a Package ?
• It is a single bound DBRM with optimized access paths
• It also contains a location identifier, a collection
identifier and a package identifier
• A package can have multiple versions, each with its
own version identifier

Advantages of Package
• Reduced bind time
• Can specify bind options at the programmer level
• Versioning
• Provides remote data access(in version DB2 V2.3 or
higher)

What is a Plan ?
• An application plan contains one or both of the
following elements:
– A list of package names
– The bound form of SQL statements taken from one
or more DBRMs.
• Every DB2 application requires an application plan.
• Plans are created using the DB2 subcommands BIND
PLAN

For the following refer handout
• List of common SQL return codes and solutions

Topics to be covered in this Session
• DB2 Utilities

DB2 System administration
DB2 UTILITIES
– Check
– Copy/Mergecopy
– Recover
– Load
– Reorg
– Runstats
– Explain

Check
• Checks the integrity of DB2 data structures
• Checks the referential integrity between two tables
and also checks DB2 indexes for consistency
• Can delete invalid rows and copies them to a exception
table
• Use CHECK DATA when loading a table without
specifying the ‘ENFORCE CONSTRAINTS’ option or after
the partial recovery of tablespaces in a referential set

Copy
• Used to create an imagecopy for the complete
tablespace or a partition of the tablespace - full
imagecopy or incremental imagecopy
• Every successful execution of COPY utility places in the
table SYSIBM.SYSCOPY, atleast one row that indicates
the status of the imagecopy

Mergecopy
• The MERGECOPY utility combines multiple incremental
image copy data sets into a new full or incremental
image copy data set

Recover
• Restore DB2 tablespaces and indexes to a specific
instance
• Data can be recovered for single page, pages that
contain I/O errors, a single partition or an entire
tablespace
• Indexes are always recovered from the actual table
data, not from image copy and log data, as in the case
of tablespace recovery
• Standard unit of recovery is a Tablespace

Load
• To accomplish bulk inserts into DB2 table
• Can replace the current data or append to it .i.e. LOAD
DATA REPLACE or LOAD DATA RESUME(S)
• If a job terminates in any phase of LOAD REPLACE the
utility has to be terminated and rerun

Load (contd...)
• If a job terminates in any phase other than
UTILINIT(which sets up and initializes the LOAD utility),
the tablespace must be first restored using the full
RECOVER, if LOG NO option of the LOAD was
mentioned. After the tablespace is restored, the error
is to be corrected, the utility terminated and the job
rerun.

Reorg
• To reorganize DB2 tables and indexes and thereby
improving their efficiency of access
• Re-clusters data, resets free space to the amount
specified in the ‘create DDL’ statement and deletes and
redefines underlying VSAM datasets for stogroup
defined objects

Runstats
• Collects statistical information for DB2 tables,
tablespaces, partitions, indexes, and columns.
• It can place this information in the catalog tables with
DB2 optimizer statistics or DBA monitoring statistics or
with all statistics that have been gathered
• It can be used on specific SQL queries without
updating the current usable statistics

Reorg Job stream
• The total reorg schedule should include a Runstats job
or step : to record current tablespace and index
statistics to DB catalog
• Two copy steps for each tablespace being reorganized :
so that data is recoverable. The second copy job is
required after the REORG if it was performed with a
LOG NO option

Reorg Job stream (contd...)
• After a REORG is run with LOG NO option, DB2 turns
on the copy pending status flag for tablespaces
specified in the REORG.
• When LOG NO parameter is specified it is better to
take a imagecopy of the tablespace being reorganized
immediately after reorg
• A REBIND job for all plans using tables in any of the
tablespaces being organized

Explain
• This feature can be used to obtain the details about
the access paths chosen by the DB2 optimizer for SQL
statements.
• Used specifically for performance monitoring.
• When EXPLAIN is requested the access paths that the
DB2 chooses are put in coded format into the table
PLAN_TABLE, which is created in the default database.

Explain (contd...)
• To EXPLAIN a single SQL statement precede that SQL
statement with the EXPLAIN Command
EXPLAIN ALL SET QUERYNO = integer
FOR SQL statement
• The other method is specifying EXPLAIN YES with the
Bind command
• Then PLAN_TABLE is to be queried to get the required
information.

Explain (contd...)
• The information provided include the type of access of
particular tables used in the SQL or Package or Plan,
the order in which the tables or joined in a JOIN,
whether SORT is required and so on
• Since the EXPLAIN results are dependent on the DB
catalog, it is better to run RUNSTATS before running a
EXPLAIN

• DB2 Security and DCL
• DB2 Locking

Data Control language
• DB2 security is provided internal to DB2 using the DCL
• The two (2) DCL statements used are
– Grant
– Revoke

Data Control language (contd...)
GRANT
• Grants privileges on different DB2 objects such as the
Tables, Views, Plans, Packages, Databases etc. to the
required set of users.
• Is used to grant Use privileges to user on requirement
• Is also used to grant system privileges to select few
users
• User with a SYSADM privilege will be responsible for
overall control of the system

Syntax : GRANT <privileges> TO <users/PUBLIC>
[WITH GRANT OPTION]
E.g. GRANT SELECT, UPDATE(NAME, NO)
ON Table EMPL To A, B, C (or PUBLIC);
GRANT EXECUTE ON PLAN PLANA To USER;

• Some table (or View) privileges are
– Select, Update, Delete and Insert
• Privileges specific to Tables are
– Alter & Index (create)
• There are no specific DROP privileges; the table can be
dropped by its owner or a SYSADM
• A user having authority to grant privilege to another,
also has the authority to grant the privilege with “with
the GRANT Option”

REVOKE
• Revoke is primarily used to revoke the privileges given
to a user on specific Objects.
• The user granting the privileges has the authority to
Revoke also.
• It is not possible to be column specific when revoking
an Update privilege

Syntax : REVOKE <privileges> FROM <user/PUBLIC>
E.g. REVOKE ALL ON Table EMPL
FROM A, B, C (or PUBLIC);
REVOKE Bind ON PLAN PLANA FROM USER;

DB2 Locking
Why Locking ?
‘Locking is used to provide multiple user access to the
same system’
How does DB2 manage locking ?
DB2 uses locking services provided by an MVS
subsystem called the IMS Resource Lock
Manager(IRLM).

DB2 Locking (contd...)
• The above is based on Transaction Processing - the
system component that provides this is
‘A TRANSACTION MANAGER’
• COMMIT & ROLLBACK are key methods of
implementing this

Explicit locking facilities
• The SQL statement LOCK TABLE
• The ISOLATION parameter on the BIND PACKAGE
command - the two possible values are RR(‘Repeatable
Read’) & CS(‘Cursor Stability’).
• CS is the value specified if the application program is
used in an online environment.
• The tablespace LOCKSIZE parameter - physically DB2
locks data in terms of pages or tables or tablespaces.
This parameter is specified in ‘CREATE or ALTER
Tablespace’ option ‘LOCKSIZE’. The options are
‘Tablespace’, ‘Table’, ‘Page’ or ‘Any’

Explicit locking facilities (contd...)
• The ACQUIRE/RELEASE parameters on the BIND PLAN
command specifies when table locks(which are
implicitly acquired by DB2) are to be acquired and
released.
• Types :
– ACQUIRE
• Use
• Allocate
– RELEASE
• Commit
• Deallocate

• DB2 Catalog & Directory
• Optimizer
• Performance tuning

Catalog Tables & the DB2 directory
• Repository for all DB2 objects - contains 43 tables
• Each table maintains data about an aspect of the DB2
environment
• The data refers to information about tablespaces,
tables, indexes, privileges, on utilities run on DB2 and
so on e.g. : SYSIBM.SYSTABLES,
SYSINDEXES/SYSCOLUMNS ......’

Catalog Tables & the DB2 directory (contd...)
• When standard DB2 SQL is used, the DB2 catalog is either
accessed or updated. e.g.. When a ‘CREATE TABLE’ statement is
issued the catalog tables SYSIBM.SYSTABLES,
SYSIBM.SYSCOLUMNS & SYSIBM.SYSFIELDS are updated.
• However the DB2 catalog is semi active only. This is because
updates to number of rows, the physical order of the rows for a
set of keys and the like are updated only after running a
RUNSTATS utility
• DB2 catalog is integrated - DB2 catalog and DB2 DBMS are
inherently bound together

Catalog Tables & the DB2 directory (contd...)
• It is nonsubvertible - DB2 catalog cannot be updated
behind DB2’s back. i.e. if a table of 10 columns is
created, it is not possible to go and change the
number of columns directly on the catalog to 15. It has
to be done using the standard SQL statements for
dropping and recreating the table

DB2 Optimizer
• Analyzes the SQL statements and determines the most
efficient way to access data - gives Physical data
independence
• It evaluates the following factors : CPU cost, I/O cost,
DB2 catalog statistics & the SQL statement
• It estimates CPU time, cost involved in applying
predicates, traversing pages and sorting

DB2 Optimizer (contd...)
• It estimates the cost of physically retrieving and
writing the data
• The information pertaining to the state of the tables
that will be accessed by the SQL statements are
provided by the Catalog

Performance Tuning
• The performance of an application can be monitored
and enhanced in the application, as well as at the
database level
• In application side the SQL’s can be tuned to make
them more efficient, and avoid redundancy
• It is better to structure the SQLs so that they perform
only the necessary operations

Performance Tuning (contd...)
• On the database side, the major enhancements can be
done to the definitions of tables, indexes & the
distribution of tablespace and indexspace
• The application run statistics are obtained from
EXPLAIN or DB2PM (DB2 Performance Monitor) report

DB2 on Mainframe

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