1. DB2 - IBM’s Relational DBMS

2. Day 1 Topics

3. 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 and the E-R model

4. 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

5. 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’.

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

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

8. 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

9. 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

10. 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

11. RELATIONAL DB CONCEPTS

12. 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

13. Relational Concepts (Terminology)
Relation : A table
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

14. 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 above remaining candidate keys that were not chosen as primary key can be alternate key.
Foreign key :An attribute of one relation that might be a primary key of another relation.

15. 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.

16. 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

17. 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

18. 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.

19. CUSTOMER Places ORDERS
E-R Model Example:
Example:
CUSTOMER Places ORDERS
ORDERS Has PRODUCTS
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)

20. E-R Model Example: (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

21. Entity As Table 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

22. Entity As Table Transforming Entity (CUSTOMER) into Table
Table ‘CUSTOMER’
Attributes - CUST_NO, CUST_NAME,
CUST-LOCATION, CUST_SSN, ORDER_NO...
Primary Key CUSTOMER_NO
Secondary Key - CUST_SSN
Foreign-Key ORDER_NO

23. Developing Relationship
For e.g.. CUSTOMER is related to Orders through ‘ORDER_NO’ which is the Foreign-key in CUSTOMER and Primary key in another table say ORDER. So basically the relationship ‘Places’ is through the ORDER_NO.
The Relationships transform into Foreign Keys.
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’.

24. Developing Relationship (contd...)
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.

25. Topics to be covered in this session
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.

26. 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

27. SQL - Features
Unlike COBOL or 4GL’s, SQL is coded without data-navigational instructions. The data 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

28. 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

29. Topics dealt with in DB2 objects
Storage Group , Databases, Tablespaces , Indexspaces
Tables , Views , Index, Synonyms , aliases

30. The DB2 Object Hierarchy

31. Storage Group
It is a named collection of direct access volumes, all of the same device type.
Each table space and each index space normally has an associated storage group.
When a given space needs to be extended, storage is acquired from the appropriate stogroup .

32. Database
A collection of logically related objects - like Tablespaces, Indexspaces, Tables etc.
It may occupy more than one disk space.
In a given database, all the spaces need not have the same storage group.

33. 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 recovery and reorganizing purpose.
Three Type of Tablespaces - Simple, Partitioned & Segmented

34. 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.

35. Segmented Tablespaces
The space within the tablespace is divided into segments.
A ‘Segment’ consists of a logically contiguous set of ‘n’ pages. ( where 4 < n < 64).
Can contain more than one stored table, but in a segmented space.
No segment is allowed to contain records for more than one table.

36. Partitioned Tablespaces
Primarily used for very large tables.
Only one table in a partitioned TS; 1 to 64 partitions/TS
It is partitioned in accordance with value ranges for single or a combination of columns. Hence these column(s) cannot be updated.
Different partitions can be stored on different storage groups for efficient access.

37. INDEXSPACES Is to an index what a tablespace is to a table.
The correspondence between index and indexspaces is one-to-one.
Indexspace are always 4KB in size.

38. TABLES
Tables are logical structures maintained by the database manager.
Tables are made up of columns and rows.
At the intersection of every column and row is a specific data item called a value.

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

40. 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.

41. 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 allow the same data to be seen by different users in different ways
In DB2 a view that is to accept an update must be derived from a single base table

42. 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.

43. DB2 Data types Char (n) 1 < n < 254 bytes
Varchar(n) variable length
Smallint 2 bytes K
Integer 4 bytes +- 2 GB
Decimal(x,y) max 31 digits
Date
Time 00:00:00
Timestamp

44. Data Definition Language
CREATE
This statement is used to create various DB2 objects.
Create Table
Syntax : For Creating a Table
CREATE TABLE <tabname>
(Col1 datatype [not null [with default]] ….),
PRIMARY KEY(Columns) /
FOREIGN KEY col1 references tablename
on delete cascade/restrict/set null
[LIKE Table name / View name]
[IN Database.Tablespace Name ]

45. Data Definition Language
Create Table Parameters
Foreign Key references dbname.table
Eg. 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

46. Data Definition Language
Create Index
Create [unique] index indexname
on tablename (col1 [desc], ….)
[using stogroup stgrp1]
[bufferpool BPn]
[close yes/no]
[freepage N]
[pctfree N]

47. Data Definition Language
Create other objects…..
CREATE VIEW <Viewname> (<columns>)
AS Subquery (Subquery - SELECT FROM other Table(s))
CREATE ALIAS <Aliasname> FOR <Tablename>
CREATE SYNONYM <Synonymname> FOR <Tablename>

48. Data Definition Language
ALTER
This statement is used for altering all DB2 objects
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

49. Data Definition Language (contd...)
DROP
This statement is used for dropping all DB2 objects
Syntax : For dropping a table
DROP TABLE <Tablename>

50. Effects of Drop table All indexes, views and synonyms are dropped.
Contents of the table are lost.
Referential constraints that involve the table are dropped.
Will not drop a table created in partitioned tablespace.

51. Topics to be covered in this session
More SQL - Insight into the DML statement Select
Simple Queries
Functions
Complex Queries
Other DML statements Insert, Update and Delete

52. 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 .

53. 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

54. 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);

55. Select clause (contd...) Like Clause
E.g. SELECT CUST_NO, CUST_NAME, CUST_ADDR
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

56. 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.

57. 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.
E.g. SELECT ORDER_NO, SUM(NO_PRODUCTS)
FROM ORDER
GROUP BY ORDER_NO
HAVING AVG(NO_PRODUCTS) < 10
ORDER BY ORDER_NO ;

58. Functions
Types are two :
Column Function
Scalar Function

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

60. 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

61. 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
1. Subqueries and
2. Joins

62. E.g. SELECT CUST_NO, CUST_NAME FROM CUSTOMER
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
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 =
(SELECT ORDER_NO FROM ORDER
WHERE NO_PRODUCTS = 5);

63. 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
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 ;
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);
E.g. SELECT CUST_NO, CUST_NAME, CUST_ADDR
FROM CUSTOMER
WHERE ORDER_NO IN
(SELECT ORDER_NO FROM ORDER
WHERE PROD_ID IN
(SELECT PROD_ID
FROM PRODUCTS
WHERE PROD_NAME = ‘NUTS’));

64. 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

65. 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

66. 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

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

68. DML statements (contd...)
DELETE
E.g. DELETE FROM Tablename
WHERE [condition ];
Single or multiple row delete or deletion of all rows

69. 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

70. 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.

71. Reference Book DB2 developer’s Guide - Craig S. Mullins
A Guide to DB C.J. Date
IBM Manuals
1. SC DB2 Application Programming and SQL Guide
2. SC DB2 SQL Reference

72. Day 2 - Topics

73. Using DB2 In An Application Program
SQL statement can be embedded in application programming languages like COBOL.

74. Comparison of a DB2/VSAM program
DB2 Tables do not require file references,such as
SELECT/ASSIGN statement in the ENVIRONMENT DIVISION.
FD statement in the DATA DIVISION.
JCL DD statements for the table(s).
Whereas, VSAM files require above file references.

75. Comparison (Contd..)
DB2 manages all physical file operations.Tables need not be opened or closed within a program, the way it is required for VSAM files.
DB2 program access data at the column level;whereas,VSAM program access data at the record level.
Error handling is better in DB2.

76. Embedded SQL 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

77. Embedded SQL 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

78. Embedded SQL Embedded SQL statements They are delimited with EXEC SQL
[………]
END-EXEC.
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.

79. Embedded SQL E.g. EXEC SQL
SELECT Empno, Empname INTO :H-empno, :H-empname
FROM EMPLOYEE
WHERE empno = 1001
END-EXEC.

80. Host variables in COBOL DB2 Program
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.
General coding format is :FieldName .

81. 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

82. Host Variables (contd...)
E.g.
EXEC SQL
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
END-EXEC.

83. About Table Declaration
DCLGEN
DCLGEN , a DB2 utility, produces host variables named as same as column name.
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.

84. DCLGEN (Contd…)
INCLUDE statement is coded to copy DCLGEN outputs into the program’s working storage section.
The general statement format is
EXEC SQL
INCLUDE source code name
END-EXEC.

85. SQL Communication Area
SQLCA
Is a source code structure made up of several fields by
means of which DB2 communicates with application
program.
Is used by DB2 to communicate to program the response
from last SQL statement executed.
Must be copied into working storage section using include
statement . The format is
EXEC SQL
INCLUDE SQLCA
END-EXEC.

86. 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).

87. DB2 Program Preparation
Pre-compiler
SOURCE
PROGRAM
MODIFIED
SOURCE
CODE
DCLGEN
BIND
PACKAGE
DBRM
COMPILER
BIND
PLAN
PACKAGE
OBJECT
CODE
PLAN
DB2
DIRECTORY
LINK-
EDIT
DB2
CATALOG
LOAD
MODULE

88. DB2 Program Execution PRECOMPILE
The SQL statements coded in the host language must first be translated
by DB2 precompiler for compilation as host language statement.
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) .

89. DB2 Program Execution 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.

90. DB2 Program Execution COMPILE & LINK
Modified precompiler COBOL output is compiled.
Compiled source is link edited to an executable load module.

91. DB2 Program Execution 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.
DB2 must be active during Bind.

92. DB2 Program Execution PLAN
A plan is an executable module containing the access path logic provided by the DB2 optimizer.
An application plan can be composed of one or more DBRMs and packages.
Every DB2 application requires an application plan.
Plans are created using the DB2 subcommands BIND PLAN.

93. DB2 Program Execution PACKAGE
It is a single bound DBRM with optimized access paths.
A package can not be executed until it is bound into a plan.Therefore it is included into the package list of a plan, which then executes.
Only the package of a particular program need to be re-bound if SQL within it has changed.

94. DB2 Program Execution DISADVANTAGES OF PLAN
If an individual DBRM needed to be re-compiled for any reason, the entire PLAN had to be re-compiled & re-bound.
Adding a new DBRM to an existing PLAN require a re-compilation & re-bind of the entire PLAN.
If multiple PLANS involved same DBRM, & if it ever needed to be re-compiled, then the all the relevant PLANS had to be re-compiled & re-bound.

95. DB2 Program Execution ADVANTAGES OF PACKAGE
Only the package of a particular program need to be re-bound if SQL within it has changed.
It is possible to add new packages to an existing plan without having the need to do a plan re-bind.
Versioning

96. DB2 Program Execution 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).

97. DB2 Program Execution BIND COMMAND
The general BIND Command Format is : -
BIND PLAN (PLAN-NAME)
MEMBER (DBRM-MEMBER-NAME,…….)
LIBRARY (DBRM-LIBRARY-NAME,…….)
ACTION (ADD / REPLACE)
RETAIN (NO / YES)
VALIDATE (RUN / BIND)
ACQUIRE (USE / ALLOCATE)
RELEASE (COMMIT / DEALLOCATE)
ISOLATION (RR / CS)
FLAG (I / W / E / C)
DB2
CATALOG
DBRM
LIBRARY
BIND
Data Base access requests
Physical Storage Characteristics
PLAN

98. Day 3 - Topics

99. Topics to be covered in this session
Cursors
Null Indicator
Application development guidelines
Isolation Levels
Performance Considerations

100. Cursors
Cursor is a mechanism by which DB2 allows an application program to retrieve a set of (multiple) rows and processes the set one row at a time.
DB2 uses cursors to navigate through a set of rows returned by an embedded SQL SELECT statement.
Cursor can be compared to a pointer.
In Application Program, if SELECT returns more than one row , then CURSOR must be used.

101. 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

102. 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.

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

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

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

106. 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

107. 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.

108. Some facts about Cursor
The cursor described in previous slides is non-scrollable cursor. It always moves sequentially forward in result table.
When cursor is opened, the cursor is positioned before the first row in result table.
When first FETCH is executed, the cursor is positioned on first row. With subsequent FETCH , it moves forward one row.
After execution of positioned DELETE or UPDATE, the cursor stays at the current row of result table.

109. Facts ..(Contd)
If CURRENT DATE, CURRENT TIME, CURRENT TIMESTAMP special registers are used in cursor,DB2 determines values in those special registers only when it OPEN the cursor. The values obtained at OPEN time are used during all subsequent fetches.
When a COMMIT is issued , the CURSOR gets closed in application program. While declaring CURSOR , WITH HOLD option can be used to avoid closing of cursor.

110. Scrollable CURSOR
To make a cursor scrollable, it is required to be declared as scrollable.
Declaring a scrollable cursor: To indicate that a cursor is scrollable, you declare it with the SCROLL keyword.
EXEC SQL DECLARE C1 SCROLL CURSOR FOR
SELECT DEPTNO,DEPTNAME,MGRNO
FROM DEPT
ORDER BYDEPTNO
END-EXEC.

111. Positions for a scrollable cursor
Keyword in FETCH statement
BEFORE Before the first row
FIRST or ABSOLUTE+1 At the first row
LAST or ABSOLUTE -1 At the last row
AFTER After the last row
ABSOLUTE 1 To an absolute row number, from before the first row forward or from after the last row backward
CURRENT At the current row
NEXT or RELATIVE +1 To the next row (default)

112. Examples for FETCH..
To fetch the fifth row of the result table in scrollable CURSOR, use a FETCH statement like this:
EXEC SQL
FETCH ABSOLUTE +5 C1
INTO :HVDEPTNO,:DEPTNAME,:MGRNO
END-EXEC. |

113. Isolation Level
The isolation level associated with an application process defines the degree of isolation of that application process from other concurrently executing application processes. The isolation level of an application process, P, therefore specifies:
The degree to which rows read and updated by P are available to other concurrently executing application processes
The degree to which update activity of other concurrently executing application processes can affect P.
The isolation level is specified as an attribute of a package and applies to the application processes that use the package. The isolation level is specified in the program preparation process.

114. Different Isolation Level
The isolation levels are:
Repeatable Read (RR)
Read Stability (RS)
Cursor Stability (CS)
Uncommitted Read (UR)

115. Isolation Level Comparison

116. 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

117. 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

118. Performance Considerations
Use the EXPLAIN utility to determine if indexes are being used
Avoid numeric conversions
Avoid character string padding
Avoid an arithmetic expression in a predicate
Do not use the SUBSTR function or concatenating columns in a predicate
Specify the same data type, precision, and scale when comparing column values against host variables and literals

119. Performance Considerations
Avoid using DISTINCT
Code predicates on indexed columns
Use ORDER BY only when sequence is important
Use BETWEEN rather than <= and >=
Use IN instead of LIKE
Joins instead of sub-queries
Use LOCK TABLE with caution
Periodically COMMIT WORK in batch update programs

120. Handling Nulls NULL Indicator
To select or Insert a column that can be set to null, it must have an indicator variable called null indicator.
To determine the value of any nullable column , a host variable and an indicator column are required.

121. Null Indicator Values.
The indicator variable contains one of the following values to indicate a columns null status:
A –ve number indicates that the column has been set to null.
The value of 2 indicates that the column has been set to null as a result of data conversion error.
A +ve or zero value indicates that the column is not null.
The indicator variable contains original length of column in case of truncation during retrieval of data into host variable not large enough.

122. Example for Null Indicator
05 H-CUST-ADD-IND PIC S9(4) COMP. :
EXEC SQL
FETCH CUR1
INTO :H-CUST-NO,
:H-CUST-NAME,
:H-CUST-ADDR1,
:H-CUST-ADDR2:H-CUST-ADD-IND
END-EXEC.

123. Few SQL Codes …
The string representation of a date-time value is not a valid date-time value
Column-name is not a column of table table-name
The order by clause is invalid because column name is not part of the result table
An update or insert value is null, but the object column column-name cannot contain null values
The cursor identified in a fetch or close statement is not open
The cursor identified in an open statement is already open

124. Few SQL Codes -504 The cursor name cursor-name is not defined
-551 The auth-id does not have the privilege to perform operation operation on object object-name
-811 The result of an embedded select statement is a table of more than one row, or the result of the sub-query of a basic predicate is more than one value
-818 The pre-compiler-generated timestamp x in the load module is different from the bind timestamp y
Unsuccessful execution caused by an unavailable resource.
The current unit of work has been rolled back due to deadlock or timeout.

125. Day 4 - Topics

126. Topics to be covered in this session
Utilities
Security and DCL
Locking
Catalog Tables
Optimizer
Performance Tuning

127. Db2 - Utilities Check Copy/MergeCopy Recover Load Reorg RunStats
Explain

128. Db2 Utilities : 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 an 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.

129. Db2 Utilities : 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.

130. Db2 Utilities : MergeCopy
The MERGECOPY utility combines multiple incremental image copy data sets into a new full or incremental image copy data set

131. Db2 Utilities : 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.

132. Db2 Utilities : 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.
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.

133. Db2 Utilities : Reorg
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.

134. Db2 Utilities : 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.

135. Db2 Utilities 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.
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.

136. Db2 Utilities : 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.
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

137. Db2 Utilities : 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.
Then PLAN_TABLE is to be queried to get the required information.

138. Db2 Security and DCL
DB2 security is provided internal to DB2 using the DCL.
The two (2) DCL statements used are:
Grant.
Revoke.

139. Db2 Security and DCL 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.

140. Db2 Security and DCL
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;

141. Db2 Security and DCL 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”.

142. Db2 Security and DCL 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.

143. Db2 Security and DCL
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;

144. 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).
The above is based on Transaction Processing - the system
component that provides this is ‘TRANSACTION MANAGER’
COMMIT & ROLLBACK are key methods of implementing
this.

145. Db2 Locking : Explicit Locking
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’.

146. Db2 Locking : Explicit Locking
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

147. Db2 Locking Db2 support locking at three levels: Table Space Table
Page
Locks cannot be taken at a lower level, without compatible higher-level lock is also being taken.

148. Db2 : Catalog Tables
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 ’

149. Db2 : Catalog Tables
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.

150. Db2 : Catalog Tables
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 .

151. Db2 : Catalog Tables
All catalogue tables have a table qualifier of ‘SYSIBM’ –
SYSIBM.SYSTABLESPACE – Table spaces in DB2
SYSIBM.SYSTABLES – All tables in DB2
SYSIBM.SYSTABAUTH – Table Authorization
SYSIBM.SYSCOLUMNS – Columns of all tables with attributes
SYSIBM.SYSVIEWS – All views definitions
SYSIBM.SYSPLAN – Plans in DB2
SYSIBM.SYSPLANAUTH – Plan Authorization
SYSIBM.SYSINDEXES – Indexes created on tables

152. 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.
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.

153. Db2 : 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.
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.

154. Questions??