Mainframe Interview Questions

Customer Information Control System (CICS) is an online transaction processing monitor from IBM that acts as an interface between the operating system and application programs to provide rapid high-volume online transaction processing.

The simplest DB2 index is the B-tree and the B-tree's top page is called the root page. The root page entries represent the upper range limits of the index and are referenced first in a search. 

There are some differences:

COBOL II supports structured programming by using in line Performs and explicit scope terminators. It introduces new features (EVALUATE, SET. TO TRUE, CALL BY CONTEXT, etc). It permits programs to be loaded and addressed above the 16-megabyte line .  It does not support many old features (READY TRACE, REPORT-WRITER, ISAM, etc.). It offers enhanced CICS support.

GROUP BY partitions the selected rows on the distinct values of the column on which you group by. HAVING selects GROUPs which match the criteria specified

While allocating KSDS Datasets, free space is declared at regular intervals at the time of initial loading. This is done because this free space is utilized for keeping the data arranged in sequence physically, even though inserted randomly.

Because SALARY is not declared to have NULLs and the employees for whom the salary is not known are also counted.

DB2 use the multiple indexes to satisfy multiple predicates in a SELECT statement that are joined by an AND or OR.

They are DEFINE CLUSTER, DATA and INDEX.