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Saturday, February 16, 2008

DB2 Basics - Quick Refernce


  • Relational Database Management System(RDBMS)

  • Universal Database(UDB)


This is one of the sub systems in Mainframes.

Any number of Sub Systems can be created in Mainframes as per the requirements.


Hierarchy of DB2 Sub system:




TS – Table Space INS – Index Space

T – Table IND – Index

V – view


Maximum storage space for a Table Space is 64 million bytes.

SQL can be used to Create, Delete, and Update and Query the Objects


SQL queries can be executed by the following techniques

  1. Application programming

  2. Tools like QMF (Query Management Facility)

SPUFI (SQL Processor User File Input)


DATA TYPES :


Integer -- 4 bytes

Small int -- 2 bytes

Char(n) – N bytes

Varchar(n) – N+2 bytes

Graph(n) – 2n bytes

Vargraph(n)– 2N+2 bytes

Date – 10 bytes

Time – 8 bytes

Timestamp – 26 bytes

NORMALIZATION :


Arranging the data in the Database in organized manner.

1NF: Avoiding multiple values or set of values in one column.

2NF: Avoiding repeated rows by defining primary key.

3NF: Separating functionally dependent and non-functionally dependent columns

Primary key :-


  • Uniquely identified row

  • Which can be formed with single or multiple columns

  • Does not allow duplicate records

  • Cannot contain Null


Foreign key : -


  • Another identifier which can be used to build relationship between the tables

  • Must be the primary key of parent table with same data type & length

  • Can consists of single or multiple columns

  • Can contain Null or duplicate rows

  • Multiple foreign keys can be defined in one table

  • Foreign key should be defined at the time of defining child table in the create command by “WITH REFERENCES” option.


CREATE TABLE ITEM(

INO INTEGER,

INAME CHAR(15),

CNO INTEGER,

PRIMARY KEY IS INO,

FOREIGN KEY IS CNO

WITH REFERENCES CUST)




REFERENCE INTEGRITY:


The relationship between two tables which can be achieved by defining foreign key.


PRIMARY KEY

FOREIGN KEY

Cannot contain Null values or duplicate rows

Can contain Null values or duplicate rows

Cannot be updated

Can be updated

Can be defined as a foreign key in other table

which must be primary key of another table

only one primary key can be defined for one table

multiple foreign keys can be defined for one table



SQL(Structured Query Language)


  • DDL (Data Definition Language)

Create, alter, drop


  • DML (Data Manipulation Language)

Insert, update, select & delete


  • DCL (Data Control Language)

Grant, Revoke


  • TCL (Transaction Control Language)

Commit, Rollback



Some SQL Quries


Static SQL for Insert: Insert into cust(cno, cname, cloc) values (10, “xyz”, “hyd”)


Dynamic SQL for Insert: Insert into cust(cno, cname, cloc) values (v1, v2, v3)

v1,v2, v3 are host variables to be defined in working storage section.


Delete from cust

Delete from cust where cno = 20


Update cust set cname = “ xyz” where cno = 20


Select cno,cname from cust

Select * from cust

Select * from, cust where cno = v1

Select * from cust wehre cno=v1 and cname =v2

Select * from cust where cno between 20 and 60

Select * from cust where cname like “%y%”



Column functions:

Select max(sal) from emp

Select min(sal) from emp

Select avg(sal) from emp

Select sum(sal) from emp



Above statement returns Null values if no row exits for specified condition

To avoid duplicate rows : select distinct cno,cname from cust

To get total no. of rows : select count(*) from cust

Above statement returns Zeros if no row exits for specified condition



SUBQUERY:


  • Query within Query

  • First inner query executes & out query executes based on the result of inner query

  • Max of 15 sub queries can be coded

  • To simplify sub queries, logic can be built with combination of COBOL + SQL statements


To retrieve second maximum salary from emp table:

Select max(sal) from emp where sal <(select max(sal) from emp)


To retrieve third maximum salary from emp table:


Select max(sal) from emp

where sal < (select max(sal) from emp

Where sal < (select max(sal) from emp))


CO-RELATED SUBQUERY:


  • For every row of outer query, inner query must executes at least once

  • First outer query executes & then inner query executes

  • Practical examples : to fine top 2,3 or n salaries


Select a. sal from emp a

where 0 = (select count(*) from emp b

Where a.sal < b.sal)



  1. -- max

  2. – 2nd max

  3. – 3rd max

  4. – 4th max


DCLGEN :


Declaration Generator . a tool to generates the equivalent COBOL variables.

Which can be used to generate host variables with equivalent data types of DB2 columns.


DB2 Table DCLGEN COBOL





Host variables:


  • Can be used to pass the data from cobol program to DB2 table or DB2 table to COBOL program.

  • When host variables are coded with sql statements it must be prefixed with : like :hv-cname.

  • Table name must be supplied as input to DCLGEN & partition dataset should be as output.

  • After creating DCLGEN variables which must be copied to application program in WORKING-STORAGE SECTION by using include command i.e.

Exec sql

Inlcude custDCL

End-exec.

  • Include & copy have the same functionality


SQLCODE :


  • Predefined numeric number which can be used to check SQL statements for successful , unsuccessful execution.

  • SQLCODE can be stored in SQLCA(SQL Communication Area)

  • Copy SQLCA in WORKING-STORAGE SECTION

  • System defined variable

  • Evaluate or if statement must be coded to check the SQLCODE immediately after SQL statement.

  • SQLCODE =00 ---- successful

= +100 --- end of table or record not found.


Sample program:


WORKING-STORAGE SECTION.


EXEC SQL

INCLUDE SQLCA

END-EXEC


EXEC SQL

INCLUDE CUSTDCL

END-EXEC.

01 WS-SQL-CODE PIC S9(4)

88 88-SUCCESS VALUE 00

88 88-NOTFOUND VALUE 100

88 88-FORIENG KEY VOILATION VALUE –532

88 88- MULITPLE ROW VALUE –811




PROCEDURE DIVISION.


UPDATE CUST

SET CNAME = :HV-CNAME

WHERE CNO=:HV-CNO

MOVE SQLCODE TO WS-SQLCODE.

EVALUE WS-SQL-CODE

WHEN 88-SUCCESS

DISPLAY “SUCCESSFULLY UPDATED”

WHEN 88-NOTFOUND

DISPLAY “ RECORD NOT FOUND”

WHEN 88-FOREIGNKEYVOILATION

DISPLAY “ FOREIGN KEY VOILATION”

WHEN OTHER

DISPLAY “ ERROR OCCURRED IN UPDATE”

STOP RUN

END-EVALUATE.

STOP RUN.



CURSOR:


To retrieve multiple rows for a given condition.


Let us take the following example:


Exec sql

Select cno,cname,cloc

into :hv-cno,:hv-cname,:hv-cloc

from cust where cloc =:hv-cloc

end-exec.

If the condition satisfy for one row it executes successfully. If the condition satisfy for multiple rows it wont work. It returns –811 as SALCODE. For this we use cursors.


  • Cursors can be used to retrieve multiple rows for a given condition

  • Cursor cycle is Declare ---> Open ----> Fetch -----> Close

  • Declare: declares or define name for cursor against a table

Can be coded in working-storage section or procedure division

For better readability code in working-storage section.

  • Open: can be used to open a cursor with rows for a given conditions inbuffer.

Retireves data in to buffer

Must be coded in the procedure division only

Where condition value must be supplied before opening a cursor.

  • Fetch: can be used to retrieve rows one by one from buffer into application prog.

Which must be coded in procedure divison after open.

Must be coded with hostvariables

No of host variables in fetch & no of columns in the declare must be same

Canbe executed multiple times using perform. i.e. till EOT or record not found which can be identified by SQLCODE = 100


  • Close : used to close the cursor

Must be coded in procedure division only

Must be executed after open statement.


Practical examples : Can be used to retrieve the data based on loc, date, products.


EXEC SQL

DECLARE C1 CURSOR FOR

SELECT CNO,CNAME FROM CUST

WHERE CNAME=:HV-CNAME

END-EXEC.

EXEC SQL

OPEN C1.

END-EXEC.

PERFORM UNTIL SQLCODE= 100

EXEC SQL

FETCH C1 INTO :HV-CNO,:HV-CNAME

END-EXEC

END-PERFORM.

EXEC SQL

CLOSE C1

END-EXEC


For Update of where current of:


  • Which can be used to update row by row when multiple rows are satisfied.

  • Before update cursor has to be declared with for update of column option.

  • Where current of cursor name option must be used with update command

  • Withhold: this option can be used to remain cursors open even after commit statement.

  • Must be coded with cursor statement


EXEC SQL

DECLARE C2 CURSOR WITH HOLD FOR

SELECT CNO,CNAME FROM CUST

WHERE CNAME=:HV-CNAME

FOR UPDATE OF CNAME

END-EXEC.

EXEC SQL

OPEN C1.

END-EXEC.

EXEC SQL

FETCH C2 INTO :HV-CNO,:HV-CNAME

END-EXEC

EXEC SQL

UPDATE CUST SET CNAME=”ABC” WHERE CURRENT OF C2.

EMD=EXEC.

EXEC SQL

CLOSE C1

END-EXEC



INDEX:


  • Index allows duplicate values

  • unique index doesn’t allow duplicate rows

  • cross reference between index table & table is called clustered index.

  • Create index in1 on cust(cno)



PRIMARY KEY


INDEX

UNIQUE INDEX

Uniquely identified row

Record identified based on the index

Records identified based on the index

No duplicated rows, no null values

Duplicate rows, null values are allowed

No duplicate rows

Can consist of single or multiple columns

Dan consist of single or multiple columns

Can consist of single or columns

This will be stored in SYSKEYS.

This is stored in SYSINDEX

This is stored in SYSINDEX




VIEWS:


CREATE VIEW CVIEW(VCNO,VCNAME,VCLOC) AS

(SELECT CNO,CNAME,CLOC FROM CUST WHERE

CNAME LIKE “%X%)


  • Logical representation of the table

  • Stored in virtual memory

  • Can be derived from single table or multiple tables

  • Views are updateable if they are derived from single table without any column functions , group by

  • Multiple views can be generated from single table.

  • Views are stored in sysviews


Advantages of Views:


  • Data security

  • Data correctness

  • Logical data independence

  • Part of the information can be visible to the sers

  • Accessing can be faster.



DELETE RULES:


  • Delete rules can be applied for delete command against Database.

  • Delete rules are 3 types

      1. on delete cascade – all matching child rows will be deleted automatically when we delete parent row.

      2. on delete restrict – all matching rows will be restricted when we delete parent row which is default.

      3. on delete set null – all matching child row will be set to null when we delete parent row.


UNION:


  • UNION is used to concatenate rows into one table from single or multiple tables.

  • Rules : no. of columns & data type of both the queries must be same. column may be different

  • UNION can be used to eliminate duplicate rows

  • UNION ALL retrieved duplicate rows also.


SELECT CNO,CNAME FROM CUST WHERE CNO=10

UNION/UNIONALL

SELECT CNO,CNAME FROM ITEM WHERE INO=20


JOINS:


  • JOINS can be used to concatenate columns from one table or multiple tables.

  • JOIN types are :

      1. left outer join : which can be used to retrieve matching, non matching rows from leftside table

      2. right outer join: which can be used to retrieve matching, non matching rows from right side table.

      3. full outer join: which can be used to retrieve matching, non matching rows from both the tables.

      4. self join or inner join : can be achieved by defining alias for the table.

EXPLAIN :


It can be used to evaluate the performance of SQL queries.

It can be used to tune SQL queries.

Input is SQL queries and output is plan-table.

For every SQL query one plan-table will generate.

All plan-tables are stored in physical seq file.




Plan table


Query

block no

Table

Name

No. of

Cols

index

no.of

indexs

owner

join type

groupby

Cpu

time


1


Cust


10


In1


1


Custc


Self


Y


10 min



DB2 CATALOG:


  • Consists of Table pace, Index space, Index, unique index, Views, Alias, synonyms, keys.

  • When we create table, the details of table are entered in Systable automatically.


SysIBM.SYSTABLE


Table Name

No.of cols

Owner name

Created by

Created date

Created time

Cust

10

Abc

Xyz

02-apr-2004

0850

Item

15

Mno

Rst

06-apr-2004

1020


SysIBM.SYSINDEX



Index name

Table Name

No.of cols

Owner name

Created by

Created date

Created time

In1

Cust

10

Abc

Xyz

02-apr-2004

0850

In2

Item

15

Mno

Rst

06-apr-2004

1020


SysIBM.SYSCOLS


Col name

Table name

Index name

Primary key

Foreign key

Cno

Cust

In1

Cno

-----

Cname

Cust

In1

Cno


Cloc

Cust

In2

cno


Ino

Item


Ino

Cno

Iname

Item


Ino

Cno

Ides

Item


Ino

cno


SysIBM.SYSKEYS: All primary & foreign keys.


Grant table syscols to all

Grant table syscols(select/delete/update) to user1,user2

Revoke table syscols from all.


CATALOG:


SYSTABLE, SYSCOL, SYSKEYS, SYSINDEX, SYSPKS, SYSFKS, SYSALIAS, SYSSYNONYMS, SYSINDEX, SYSVIEWS,SYSTABLESPACE, SYSINDEXSPACE.


PRECOMPILATION PROCESS:


Pre compiler takes COBOL+DB2 program as input & generates DBRM which will be stored in userdefined PDS as separate member of Recln=80


DSNHPC --- IBM supplied utility used for precompilation.


Precompiler functions:


  • Separates SQL & COBOL statements

  • Check SQL syntaxs

  • Replace all SQL statements with host language call statements in the compiled program.

  • Which generates timestamp tokens


BIND:


BIND takes DBRM as input & generate package & application plan. The package will be loaded to the directory. Plan will be loaded to sysplans.


Bind functions:


  • Checks authorization for SQL statement

  • Checks the syntax errors of SQL statements like

  1. Missing co name in the select list & used in order by & group by

  2. Mismatch columns host variables

  3. Data type mismatch of columns & host variables

  4. Indicator variables not declared

  5. Data truncation.


BIND SUBCOMPONANTS/PARAMETERS:


  1. OPTIMIZER:

    • It generates optimized access path by analyzing the statistics of SQL statements which will be stored.

    • RUNSTATS utility is one of the ISPF panel option which is stored in DB2 defaults option.

    • Optimized path is stored in package which is not executable module.


  1. ISOLATION LEVEL:

Which can be used to lock the database at the time of executing SQL statements.


Cusrsor stability(CS): It acquires the address of a row. Sets the pointer to a specified row based on SQL query & acquires the lock against that row. Then releases the klock after the transaction before commit.


Repeatable Read(RR): which acquires the address of a row & acquire lock against the page(1 page -4024 bytes) & then released the lock after the commit statements.


Default is RR.


  1. RUNTIME SUPERVISOR:

Which is to oversee execution of SQL statements.

Statistics like no of tables, columns, indexes, keys


  1. PLAN/APPLICATION PLAN:

It consists of executable module which is actual output of SQL statements which must be specified in the RUNJCL to execute SQL queries if the program is batch program. If the program is online which must be specified in RCT. Application plan will be loaded to load module with time stamp tokens.


COBOL COMPILATION:

The compiler takes COBOL statement as input to generate object program, & loaded to the load module by line/edit with time stamp tokens.


UTILITIES USED:


DSNHPC : system utility pre compiler.

IKJEFT01 or IKJEFT01B --- BIND /Run Cob-DB2 Program

IGYCRCTL or IKFCBLOO --- COBOL compilation

IEWL or HEWL --- link/edit



INTERVIEW QUESTIONS: (watch this space for more info on below Qns)


  1. What is RI ? where did u use RI in your project? Explain with example?

  2. What is the difference between primary key, foreign key, index & unique index?

  3. Can we create index when table has duplicate rows?

  4. Can we create unique index when table has duplicate rows?

  5. Can we create index or unique index on empty table?

  6. What happens to the package when index is dropped? What’s the process or steps to be taken?

  7. How to delete package?

  8. Where package is stored? How to retrieve package?

  9. Difference between plan & package?

  10. What are the steps to be taken when SQL statements are changed without changing any COBOL statements?

  11. Do we need to pre compile when index is dropped?

  12. Can we bind when table is dropped?

  13. Can optimized access path consist of multiple DBRMS.

  14. What is the significance of timestamp tokens?

  15. What is the significance of normalization?

  16. Where do we specify run program, plan name, library & DB2 subsystem

  17. IBM supplied utility to run COBOL + DB2

  18. What is difference between DB2 & COBOL files & give some example for COBOL files & DB2 tables related to your project?

  19. Can we load data from sequential file to table or table to sequential file?

  20. What are the steps to be followed to develop DB2+ COBOL program?

  21. Can we prepare a program/compile when DB2 system is down?

  22. How to identify DB2 test or production system by seeing run JCL?

  23. What is the output of explain?

  24. What is the difference between correlated sub query & sub query?

  25. How to find 4th max sal?

  26. How to find nth max sal?

  27. How to evaluate SQLcodes & where it is stored?

  28. How to count total no of unique rows from the table?

  29. How to sum repeated rows?

  30. How to write a cobol program for above query? Retrieve row by row & use cobol logic to sum repeated rows?

  31. What is the significance of DCLGEN?

  32. Where DCLGEN is stored?

  33. Difference between join & union?

  34. difference between UNION & UNIONALL?

  35. Can be have different col names in union?

  36. How do u evaluate/tune/analyze SQL queries?

  37. What are the JCL utilities for compile, pre compile, bind & link edit?

  38. Wha5t is the significance of isolated levels?

  39. Can we alter foreign key?

  40. Can we alter primary key?

  41. Can we alter data type & length?

  42. What are the equivalent cobol variables for varchar?

  43. What is the time stamp & its format?




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