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Q:

What is RUNSTATS?

Answer

A DB2 utility used to collect statistics about the data values  in tables which can be used   by the optimizer to decide the access path. It also collects statistics used for space   management. These statistics are stored in DB2 catalog tables.

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Subject: Mainframe Interview

Q:

How does DB2 determine what lock- size to use?

Answer

1. Based on the lock-size given while creating the table space


2. Programer can direct the DB2 what lock-size to use


3. If lock - size ANY is specified, DB2 usually chooses a lock-size of PAGE

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Subject: Mainframe Interview

Q:

EXPLAIN has output with MATCHCOLS = 0. What does it mean?

Answer

a nonmatching index scan if ACCESSTYPE = 1


 

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Subject: Mainframe Interview

Q:

What is DCLGEN?

Answer

DeCLarations GENerator : used to create the host language copy books for the table    definitions. Also creates the DECLARE table.

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Subject: Mainframe Interview

Q:

What is a cursor ? Why should it be used in DB2?

Answer

Cursor is a programming device that allows the SELECT to find a set of rows but return them one at a time. Cursor should be used because the host language  can deal with only one row at a time.

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Subject: Mainframe Interview

Q:

What is UNION , UNION ALL?

Answer

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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Subject: Mainframe Interview

Q:

How do you eliminate duplicate values in DB2 SELECT?

Answer

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;


 

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Subject: Mainframe Interview

Q:

What is Marshalling?

Answer

Marshalling is the process of gathering data from one or more applications or non-contiguous sources in computer storage, putting the data pieces into a message buffer, and organizing or converting the data into a format that is prescribed for a particular receiver or programming interface.  

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Subject: Microsoft Interview