Mainframe Interview Questions

IDMS uses record locks to prevent another run-unit from updating the same record.

Use the SORTWK01, SORTWK02,..... dd names in the step. Number of sort datasets depends on the volume of data being sorted, but a minimum of 3 is required.

The following are the ways of initiating a CICS transaction.

1. By entering Transaction Id

2. By Start command

3. By Return Trans Id (as in pseudo - conversation)

4. By Registering Tran ID in plt so that it will be automaticaly dusring CICS start

5. By ATI (Automatic task initiation)

6.PF & PA keys as defined in PCT

Use SELECT DISTINCT ..... in DB2 query

The DISTINCT keyword can be used to return only distinct (different) values.

Syntax:

     SELECT DISTINCT column1,column2

      FROM table_name;

CURSOR STABILITY:

- CS is a row level locking

- Acquires an exclusive lock on the row that is to be updated

- When the control is moved to the next updatable row, the lock is released

REPEATABLE READ:

- RR is a page level locking

- Acquires an exclusive lock on the entire page which is the source of row availability

- When the control is moved to the next updatable page the lock is released

SELECT * FROM table_name ORDER BY column_name desc Fetch first 5 rows only;

Both these are used to combine the results of different SELECT statements.

    UNION       - Selects only distinct values 

    UNION ALL - Selects duplicate values also

Syntax:

    SELECT column_name(s) FROM table1

    UNION / UNION ALL

    SELECT column_name(s) FROM table2;

Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

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