Mainframe Interview Questions

No difference. There is a difference between obtain first and obtain next for an area sweep, but not when current on the owner in a set.

a nonmatching index scan if ACCESSTYPE = 1

- If the table structure is changed ( a field is added ), the program will have to be modified.

- Program might retrieve the columns which it might not use, leading on I/O over head.

- The chance of an index only scan is lost.

Currency is the location within the database during run-unit execution.

There are four levels of currency:

- Current of run-unit is the record occurrence of the last successful find or obtain;

- Current of record type is for the most recent of each record type;

- Current of record set is the most recent within each set 

- Current of area is within each area.

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

SELECT statement has resulted in retrieval of more than one row.

VSAM acts as an interface between Application program & Operating System.

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;