5) How do you retrieve the first 5 characters of FIRSTNAME column of DB2 table EMP
SQL Query : SELECT SUBSTR(FIRSTNAME,1,5) FROM EMP;
6) What are aggregate functions?
Bulit-in mathematical functions for use in SELECT clause.
7) Can you use MAX on a CHAR column?
8) My SQL statement SELECT AVG(SALARY) FROM EMP yields inaccurate results.
Because SALARY is not declared to have NULLs and the employees for whom the
salary is not known are also counted.
9) How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a
SELECT FIRSTNAME || � � || LASTNAME FROM EMP;
10) What is the use of VALUE function?
1. Avoid -ve SQLCODEs by handling nulls and zeroes in computations
2. Substitute a numeric value for any nulls used in computation
11) What is UNION,UNION ALL? �
UNION : eliminates duplicates
UNION ALL: retains duplicates
Both these are used to combine the results of different SELECT
Suppose I have five SQL SELECT statements connected by UNION/UNION ALL, how
many times should I specify UNION to eliminate the duplicate rows? -
12) What is the restriction on using UNION in embedded SQL?
It has to be in a CURSOR.
13) In the WHERE clause what is BETWEEN and IN? �
BETWEEN supplies a range of values while IN supplies a list of values.
14) Is BETWEEN inclusive of the range values specified? �
15) What is 'LIKE' used for in WHERE clause? What are the wildcard
LIKE is used for partial string matches. �%� ( for a string of any character
) and �_� (for any single character ) are the two wild card characters.
16) When do you use a LIKE statement?
To do partial search e.g. to search employee by name, you need not specify
the complete name; using LIKE, you can search for partial string matches.
17) What is the meaning of underscore ( �_� ) in the LIKE statement? �
Match for any single character.
18) What do you accomplish by GROUP BY ... HAVING clause? �
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
19) Consider the employee table with column PROJECT nullable. How can you get
a list of employees who are not assigned to any project?
WHERE PROJECT IS NULL;
20) What is the result of this query if no rows are selected:
21) Why SELECT * is not preferred in embedded SQL programs?
For three reasons:
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
The chance of an index only scan is lost.
What are correlated subqueries? -
A subquery in which the inner ( nested ) query refers back to the table in
the outer query. Correlated subqueries must be evaluated for each qualified row
of the outer query that is referred to.
22) What are the issues related with correlated subqueries? �
DB2 Interview Questions - PART II
23) What is a cursor? why should it be used? �
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
24) How would you retrieve rows from a DB2 table in embedded SQL? �
Either by using the single row SELECT statements, or by using the CURSOR.
Apart from cursor, what other ways are available to you to retrieve a row
from a table in embedded SQL? -
Single row SELECTs.
25) Where would you specify the DECLARE CURSOR statement? �
See answer to next question.
26) How do you specify and use a cursor in a COBOL program? �
Use DECLARE CURSOR statement either in working storage or in procedure
division(before open cursor), to specify the SELECT statement. Then use OPEN,
FETCH rows in a loop and finally CLOSE.
27) What happens when you say OPEN CURSOR?
If there is an ORDER BY clause, rows are fetched, sorted and made available
for the FETCH statement. Other wise simply the cursor is placed on the first
28) Is DECLARE CURSOR executable?
29) Can you have more than one cursor open at any one time in a program ? �
30) When you COMMIT, is the cursor closed? - drona db2 interview questions
31) How do you leave the cursor open after issuing a COMMIT? ( for DB2 2.3 or
above only )
Use WITH HOLD option in DECLARE CURSOR statement. But, it has not effect in
psuedo-conversational CICS programs.
32) Give the COBOL definition of a VARCHAR field.
A VARCHAR column REMARKS would be defined as follows:
49 REMARKS-LEN PIC S9(4) USAGE COMP.
49 REMARKS-TEXT PIC X(1920).
33) What is the physical storage length of each of the following DB2 data
DATE, TIME, TIMESTAMP?
34) What is the COBOL picture clause of the following DB2 data types:
DATE, TIME, TIMESTAMP?
DATE: PIC X(10)
TIME : PIC X(08)
TIMESTAMP: PIC X(26)
35) What is the COBOL picture clause for a DB2 column defined as
DECIMAL(11,2)? - Ramesh
PIC S9(9)V99 COMP-3.
Note: In DECIMAL(11,2), 11 indicates the size of the data type and 2
indicates the precision.
36) What is DCLGEN ? -
DeCLarations GENerator: used to create the host language copy books for the
table definitions. Also creates the DECLARE table.
37) What are the contents of a DCLGEN? -
1. EXEC SQL DECLARE TABLE statement which gives the layout of the table/view
in terms of DB2 datatypes.
2. A host language copy book that gives the host variable definitions for the
38) Is it mandatory to use DCLGEN? If not, why would you use it at all? -
It is not mandatory to use DCLGEN.
Using DCLGEN, helps detect wrongly spelt column names etc. during the
pre-compile stage itself ( because of the DECLARE TABLE ). DCLGEN being a tool,
would generate accurate host variable definitions for the table reducing chances
39) Is DECLARE TABLE in DCLGEN necessary? Why it used?
It not necessary to have DECLARE TABLE statement in DCLGEN. This is used by
the pre-compiler to validate the table-name, view-name, column name etc., during
40) Will precompile of an DB2-COBOL program bomb, if DB2 is down?
No. Because the precompiler does not refer to the DB2 catalogue
41) How is a typical DB2 batch pgm executed ?
1. Use DSN utility to run a DB2 batch program from native TSO. An example is
RUN PROGRAM(EDD470BD) PLAN(EDD470BD) LIB('ED 01T.OBJ.LOADLIB')
2. Use IKJEFT01 utility program to run the above DSN command in a JCL.
Assuming that a site�s standard is that pgm name = plan name, what is the
easiest way to find out which pgms are affected by change in a table�s structure
Query the catalogue tables SYSPLANDEP and SYSPACKDEP.
42) Name some fields from SQLCA.
SQLCODE, SQLERRM, SQLERRD
43) How can you quickly find out the # of rows updated after an update
Check the value stored in SQLERRD(3).
44) What is EXPLAIN? � drona questions
EXPLAIN is used to display the access path as determined by the optimizer for
a SQL statement. It can be used in SPUFI (for single SQL statement ) or in BIND
step (for embedded SQL ).
45) What do you need to do before you do EXPLAIN?
Make sure that the PLAN_TABLE is created under the AUTHID.
46) Where is the output of EXPLAIN stored? �
47) EXPLAIN has output with MATCHCOLS = 0. What does it mean? �
a nonmatching index scan if ACCESSTYPE = I.
48) How do you do the EXPLAIN of a dynamic SQL statement?
1. Use SPUFI or QMF to EXPLAIN the dynamic SQL statement
2. Include EXPLAIN command in the embedded dynamic SQL statements
49) How do you simulate the EXPLAIN of an embedded SQL statement in
SPUFI/QMF? Give an example with a host variable in WHERE clause.)
Use a question mark in place of a host variable ( or an unknown value ).
WHERE EMP_SALARY > ?
DB2 Interview Questions - PART III
50) What are the isolation levels possible ? �
CS: Cursor Stability
RR: Repeatable Read
51) What is the difference between CS and RR isolation levels?
CS: Releases the lock on a page after use
RR: Retains all locks acquired till end of transaction
52) Where do you specify them ?
ISOLATION LEVEL is a parameter for the bind process.
53) When do you specify the isolation level? How?
During the BIND process. ISOLATION ( CS/RR )...
I use CS and update a page. Will the lock be released after I am done with
54) What are the various locking levels available?
PAGE, TABLE, TABLESPACE
55) How does DB2 determine what lock-size to use?
1. Based on the lock-size given while creating the tablespace
2. Programmer can direct the DB2 what lock-size to use
3. If lock-size ANY is specified, DB2 usually chooses a lock-size of
56) What are the disadvantages of PAGE level lock? - RAMESH www.mainframetutorials.com
High resource utilization if large updates are to be done
57) What is lock escalation?
Promoting a PAGE lock-size to table or tablespace lock-size when a
transaction has acquired more locks than specified in NUMLKTS. Locks should be
taken on objects in single tablespace for escalation to occur.