IBM DB2 Interview Questions - An interviewhelper.org blog

What do you mean by NOT NULL WITH DEFAULT When will you use it

2009-03-06T22:28:00.000-08:00

Question :What do you mean by NOT NULL WITH DEFAULT? When will you use it?
Answer :This column cannot have nulls and while insertion, if no value is supplied then it wil have zeroes, spaces or date/time depending on whether it is numeric, character or date/time. Use it when you do not want to have nulls but at the same time cannot give values all the time you insert this row

What is the difference between SYNONYM and ALIAS

2009-03-06T22:27:00.000-08:00

Question :What is the difference between SYNONYM and ALIAS?
Answer :SYNONYM: is dropped when the table or tablespace is dropped. Synonym is available only to the creator. ALIAS: is retained even if table or tablespace is dropped. ALIAS can be created even if the table does not exist. It is used mainly in distributed environment to hide the location info from programs. Alias is a global object & is available to all.

What is index cardinality

2009-03-06T22:26:00.002-08:00

Question :What is index cardinality? ?
Answer :The number of distinct values a column or columns contain. 103) What is a synonym ? Synonym is an alternate name for a table or view used mainly to hide the leading qualifier of a table or view.. A synonym is accessible only by the creator.

What is filter factor

2009-03-06T22:26:00.001-08:00

Question :What is filter factor?
Answer :one divided by the number of distinct values of a column.

What are simple, segmented and partitioned table spaces

2009-03-06T22:24:00.000-08:00

Question :What are simple, segmented and partitioned table spaces ?
Answer :Simple Tablespace: Can contain one or more tables Rows from multiple tables can be interleaved on a page under the DBAs control and maintenance Segmented Tablespace: Can contain one or more tables Tablespace is divided into segments of 4 to 64 pages in increments of 4 pages. Each segment is dedicated to single table. A table can occupy multiple segments Partitioned Tablespace: Can contain one table Tablespace is divided into parts and each part is put in a separate VSAM dataset.

What is FREEPAGE and PCTFREE in TABLESPACE creation

2009-03-06T22:23:00.002-08:00

Question :What is FREEPAGE and PCTFREE in TABLESPACE creation?
Answer :PCTFREE: percentage of each page to be left free FREEPAGE: Number of pages to be loaded with data between each free page

What is an inner join, and an outer join

2009-03-06T22:23:00.001-08:00

Question :What is an inner join, and an outer join ?
Answer :Inner Join: combine information from two or more tables by comparing all values that meet the search criteria in the designated column or columns of on e table with all the clause in corresponding columns of the other table or tables. This kind of join which involve a match in both columns are called inner joins. Outer join is one in which you want both matching and non matching rows to be returned. DB2 has no specific operator for outer joins, it can be simulated by combining a join and a correlated sub query with a UNION.

What are the 4 environments which can access DB2

2009-03-06T22:21:00.000-08:00

Question :What are the 4 environments which can access DB2 ?
Answer :TSO, CICS, IMS and BATCH

If I have a view which is a join of two or more tables, can this view be updateable

2009-03-06T22:20:00.000-08:00

Question :If I have a view which is a join of two or more tables, can this view be updateable? ?
Answer :No.

Are views updateable

2009-03-06T22:19:00.000-08:00

Question :Are views updateable ?
Answer :Not all of them. Some views are updateable e.g. single table view with all the fields or mandatory fields. Examples of non-updateable views are views which are joins, views that contain aggregate functions(such as MIN), and views that have GROUP BY clause.

What does the sqlcode of -818 pertain to

2009-03-06T22:18:00.002-08:00

Question :What does the sqlcode of -818 pertain to?
Answer :This is generated when the consistency tokens in the DBRM and the load module are different.

What is sqlcode -811

2009-03-06T22:18:00.001-08:00

Question :What is sqlcode -811?
Answer :SELECT statement has resulted in retrieval of more than one row.

What is sqlcode -922

2009-03-06T05:33:00.000-08:00

Question :What is sqlcode -922 ?
Answer :Authorization failure

What is the difference between primary key & unique index

2009-03-06T05:31:00.000-08:00

Question :What is the difference between primary key & unique index?
Answer :Primary : a relational database constraint. Primary key consists of one or more columns that uniquely identify a row in the table. For a normalized relation, there is one designated primary key. Unique index: a physical object that stores only unique values. There can be one or more unique indexes on a table.

How many clustering indexes can be defined for a table

2009-03-06T04:46:00.000-08:00

Question :How many clustering indexes can be defined for a table?
Answer :Only one.

What is a clustering index

2009-03-06T04:45:00.000-08:00

Question :What is a clustering index ? ?
Answer :Causes the data rows to be stored in the order specified in the index. A mandatory index defined on a partitioned table space.

What is QUIESCE

2009-03-06T04:41:00.000-08:00

Question :What is QUIESCE?
Answer :A QUIESCE flushes all DB2 buffers on to the disk. This gives a correct snapshot of the database and should be used before and after any IMAGECOPY to maintain consistency.

What is CHECK PENDING

2009-03-06T04:40:00.000-08:00

Question :What is CHECK PENDING ?
Answer :When a table is LOADed with ENFORCE NO option, then the table is left in CHECK PENDING status. It means that the LOAD utility did not perform constraint checking.

What is COPY PENDING status

2009-03-06T04:25:00.000-08:00

Question :What is COPY PENDING status?
Answer :A state in which, an image copy on a table needs to be taken, In this status, the table is available only for queries. You cannot update this table. To remove the COPY PENDING status, you take an image copy or use REPAIR utility.

What is IMAGECOPY

2009-03-06T03:36:00.000-08:00

Question :What is IMAGECOPY?
Answer :It is full backup of a DB2 table which can be used in recovery.

What is REORG? When is it used

2009-03-06T03:35:00.000-08:00

Question :What is REORG? When is it used?
Answer :REORG reorganizes data on physical storage to reclutser rows, positioning overflowed rows in their proper sequence, to reclaim space, to restore free space. It is used after heavy updates, inserts and delete activity and after segments of a segmented tablespace have become fragmented.

Give some example of statistics collected during RUNSTATS

2009-03-06T03:33:00.000-08:00

Question :Give some example of statistics collected during RUNSTATS?
Answer :# of rows in the table Percent of rows in clustering sequence # of distinct values of indexed column # of rows moved to a nearby/farway page due to row length increase

When will you chose to run RUNSTATS

2009-03-06T03:30:00.000-08:00

Question :When will you chose to run RUNSTATS?
Answer :After a load, or after mass updates, inserts, deletes, or after REORG.

What is RUNSTATS

2009-03-06T03:29:00.000-08:00

Question :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.

How do you insert a record with a nullable column

2009-03-06T03:28:00.000-08:00

Question :How do you insert a record with a nullable column?
Answer :To insert a NULL, move -1 to the null indicator To insert a valid value, move 0 to the null indicator

What does it mean if the null indicator has -1, 0, -2

2009-03-06T03:27:00.000-08:00

Question :What does it mean if the null indicator has -1, 0, -2?
Answer :-1 : the field is null 0 : the field is not null -2 : the field value is truncated

What is the picture clause of the null indicator variable

2009-03-06T03:25:00.000-08:00

Question :What is the picture clause of the null indicator variable?
Answer :S9(4) COMP.

How do you retrieve the data from a nullable column

2009-03-06T03:24:00.000-08:00

Question :How do you retrieve the data from a nullable column?
Answer :Use null indicators. Syntax ... INTO :HOSTVAR:NULLIND

How does DB2 store NULL physically? as an extra-byte prefix to the column value. physically, the nul prefix is Hex ?00? if the value is present and He

2009-03-06T03:21:00.000-08:00

Question :How does DB2 store NULL physically? as an extra-byte prefix to the column value. physically, the nul prefix is Hex ?00? if the value is present and Hex ?FF?
Answer :It is not.

Suppose I have a program which uses a dynamic SQL and it has been performing well till now. Off late, I find that the performance has deteriorated. Wh

2009-03-06T03:20:00.000-08:00

Question :Suppose I have a program which uses a dynamic SQL and it has been performing well till now. Off late, I find that the performance has deteriorated. What happened? ?
Answer :Probably RUN STATS is not done and the program is using a wrong index due to incorrect stats. Probably RUNSTATS is done and optimizer has chosen a wrong access path based on the latest statistics.

When is the access path determined for dynamic SQL

2009-03-06T03:19:00.000-08:00

Question :When is the access path determined for dynamic SQL?
Answer :At run time, when the PREPARE statement is issued.

What is dynamic SQL

2009-03-06T03:18:00.000-08:00

Question :What is dynamic SQL?
Answer :Dynamic SQL is a SQL statement created at program execution time.

Lot of updates have been done on a table due to which indexes have gone haywire. What do you do

2009-03-06T03:16:00.000-08:00

Question :Lot of updates have been done on a table due to which indexes have gone haywire. What do you do?
Answer :Looks like index page split has occurred. DO a REORG of the indexes.

How would you print the output of an SQL statement from SPUFI

2009-03-06T03:15:00.000-08:00

Question :How would you print the output of an SQL statement from SPUFI?
Answer :Print the output dataset.

What are the 2 sqlcodes that are returned

2009-03-06T03:10:00.000-08:00

Question :What are the 2 sqlcodes that are returned?
Answer :100 ( for successful completion of the query ), 0 (for successful COMMIT if AUTOCOMMIT is set to Yes).

What is a collection? a user defined name that is the anchor for packages

2009-03-06T03:08:00.000-08:00

Question :What is a collection? a user defined name that is the anchor for packages?
Answer :It has not physical existence. Main usage is to group packages. In SPUFI suppose you want to select max. of 1000 rows , but the select returns only 200 rows.

What are the advantages of using a PACKAGE

2009-03-06T03:06:00.000-08:00

Question :What are the advantages of using a PACKAGE?
Answer :1. Avoid having to bind a large number of DBRM members into a plan 2. Avoid cost of a large bind 3. Avoid the entire transaction being unavailable during bind and automatic rebind of a plan 4. Minimize fallback complexities if changes result in an error.

What are PACKAGES

2009-03-06T03:05:00.000-08:00

Question :What are PACKAGES ?
Answer :They contain executable code for SQL statements for one DBRM.

What happens to the PLAN if index used by it is dropped

2009-03-06T02:14:00.000-08:00

Question :What happens to the PLAN if index used by it is dropped?
Answer :Plan is marked as invalid. The next time the plan is accessed, it is rebound.

What else is there in the PLAN apart from the access path

2009-03-06T02:13:00.000-08:00

Question :What else is there in the PLAN apart from the access path?
Answer :PLAN has the executable code for the SQL statements in the host program

What is ACQUIRE/RELEASE in BIND

2009-03-06T02:11:00.000-08:00

Question :What is ACQUIRE/RELEASE in BIND?
Answer :Determine the point at which DB2 acquires or releases locks against table and tablespaces, including intent locks.

What is a DBRM, PLAN

2009-03-06T02:10:00.000-08:00

Question :What is a DBRM, PLAN ?
Answer :DBRM: DataBase Request Module, has the SQL statements extracted from the host language program by the pre-compiler. PLAN: A result of the BIND process. It has the executable code for the SQL statements in the DBRM.

What is ALTER

2009-03-06T02:09:00.000-08:00

Question :What is ALTER ? ?
Answer :SQL command used to change the definition of DB2 objects.

Can I use LOCK TABLE on a view

2009-03-06T02:06:00.000-08:00

Question :Can I use LOCK TABLE on a view?
Answer :No. To lock a view, take lock on the underlying tables.

What are the various locks available

2009-03-06T02:05:00.000-08:00

Question :What are the various locks available?
Answer :SHARE, EXCLUSIVE, UPDATE

What is lock escalation

2009-03-06T02:04:00.000-08:00

Question :What is lock escalation?
Answer :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.

What are the disadvantages of PAGE level lock

2009-03-06T02:03:00.000-08:00

Question :What are the disadvantages of PAGE level lock?
Answer :High resource utilization if large updates are to be done

How does DB2 determine what lock-size to use

2009-03-06T02:01:00.000-08:00

Question :How does DB2 determine what lock-size to use?
Answer :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 PAGE

What are the various locking levels available

2009-03-06T02:00:00.000-08:00

Question :What are the various locking levels available?
Answer :PAGE, TABLE, TABLESPACE

When do you specify the isolation level? How

2009-03-06T01:59:00.000-08:00

Question :When do you specify the isolation level? How?
Answer :During the BIND process. ISOLATION ( CS/RR )... I use CS and update a page. Will the lock be released after I am done with that page? No.

Where do you specify them

2009-03-06T01:58:00.000-08:00

Question :Where do you specify them ?
Answer :ISOLATION LEVEL is a parameter for the bind process.

What is the difference between CS and RR isolation levels

2009-03-06T01:57:00.000-08:00

Question :What is the difference between CS and RR isolation levels?
Answer :CS: Releases the lock on a page after use RR: Retains all locks acquired till end of transaction

What are the isolation levels possible

2009-03-06T01:56:00.000-08:00

Question :What are the isolation levels possible ?
Answer :CS: Cursor Stability RR: Repeatable Read

How do you simulate the EXPLAIN of an embedded SQL statement in SPUFI/QMF? Give an example with a host variable in WHERE clause.)

2009-03-06T01:55:00.000-08:00

Question :How do you simulate the EXPLAIN of an embedded SQL statement in SPUFI/QMF? Give an example with a host variable in WHERE clause.) ?
Answer :Use a question mark in place of a host variable ( or an unknown value ). e.g. SELECT EMP_NAME FROM EMP WHERE EMP_SALARY > ?

How do you do the EXPLAIN of a dynamic SQL statement

2009-03-06T01:54:00.002-08:00

Question :How do you do the EXPLAIN of a dynamic SQL statement?
Answer :1. Use SPUFI or QMF to EXPLAIN the dynamic SQL statement 2. Include EXPLAIN command in the embedded dynamic SQL statements

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

2009-03-06T01:54:00.001-08:00

Question :EXPLAIN has output with MATCHCOLS = 0. What does it mean? ?
Answer :a nonmatching index scan if ACCESSTYPE = I.

Where is the output of EXPLAIN stored

2009-03-06T01:52:00.001-08:00

Question :Where is the output of EXPLAIN stored?
Answer :In userid.PLAN_TABLE

What do you need to do before you do EXPLAIN

2009-03-06T01:51:00.001-08:00

Question :What do you need to do before you do EXPLAIN?
Answer :Make sure that the PLAN_TABLE is created under the AUTHID.

What is EXPLAIN

2009-03-06T01:46:00.000-08:00

Question :What is EXPLAIN?
Answer :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 ).

How can you quickly find out the # of rows updated after an update statement

2009-03-06T01:43:00.000-08:00

Question :How can you quickly find out the # of rows updated after an update statement?
Answer :Check the value stored in SQLERRD(3).

How is a typical DB2 batch pgm executed

2009-03-06T01:42:00.000-08:00

Question :How is a typical DB2 batch pgm executed ?
Answer :1. Use DSN utility to run a DB2 batch program from native TSO. An example is shown: DSN SYSTEM(DSP3) RUN PROGRAM(EDD470BD) PLAN(EDD470BD) LIB('ED 01T.OBJ.LOADLIB') END 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.

Will precompile of an DB2-COBOL program bomb, if DB2 is down

2009-03-06T01:41:00.000-08:00

Question :Will precompile of an DB2-COBOL program bomb, if DB2 is down?
Answer :No. Because the precompiler does not refer to the DB2 catalogue tables.

Is DECLARE TABLE in DCLGEN necessary Why it used

2009-03-06T01:40:00.001-08:00

Question :Is DECLARE TABLE in DCLGEN necessary? Why it used?
Answer :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 pre-compile.

Is it mandatory to use DCLGEN? If not, why would you use it at all

2009-03-05T22:48:00.002-08:00

Question :Is it mandatory to use DCLGEN? If not, why would you use it at all?
Answer :- 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 of error.

What are the contents of a DCLGEN

2009-03-05T22:48:00.001-08:00

Question :What are the contents of a DCLGEN?
Answer :- 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 column names.

What is DCLGEN

2009-03-05T22:47:00.000-08:00

Question :What is DCLGEN ?
Answer :- DeCLarations GENerator: used to create the host language copy books for the table definitions. Also creates the DECLARE table.

What is the COBOL picture clause for a DB2 column defined as DECIMAL(11,2)

2009-03-05T22:46:00.000-08:00

Question :What is the COBOL picture clause for a DB2 column defined as DECIMAL(11,2)?
Answer :- PIC S9(9)V99 COMP-3. Note: In DECIMAL(11,2), 11 indicates the size of the data type and 2 indicates the precision.

What is the COBOL picture clause of the following DB2 data types: DATE, TIME, TIMESTAMP

2009-03-05T22:45:00.000-08:00

Question :What is the COBOL picture clause of the following DB2 data types: DATE, TIME, TIMESTAMP?
Answer :DATE: PIC X(10) TIME : PIC X(08) TIMESTAMP: PIC X(26)

What is the physical storage length of each of the following DB2 data types: DATE, TIME, TIMESTAMP

2009-03-05T22:44:00.001-08:00

Question :What is the physical storage length of each of the following DB2 data types: DATE, TIME, TIMESTAMP?
Answer :DATE: 4bytes TIME: 3bytes TIMESTAMP: 10bytes

Give the COBOL definition of a VARCHAR field. A VARCHAR column REMARKS would be defined as follows: ...

2009-03-05T22:41:00.002-08:00

Question :Give the COBOL definition of a VARCHAR field. A VARCHAR column REMARKS would be defined as follows: ...
Answer :10 REMARKS. 49 REMARKS-LEN PIC S9(4) USAGE COMP. 49 REMARKS-TEXT PIC X(1920).

How do you leave the cursor open after issuing a COMMIT? ( for DB2 2.3 or above only )

2009-03-05T22:41:00.001-08:00

Question :How do you leave the cursor open after issuing a COMMIT? ( for DB2 2.3 or above only )
Answer :Use WITH HOLD option in DECLARE CURSOR statement. But, it has not effect in psuedo-conversational CICS programs.

When you COMMIT, is the cursor closed

2009-03-05T22:39:00.001-08:00

Question :When you COMMIT, is the cursor closed?
Answer :Yes.

Can you have more than one cursor open at any one time in a program

2009-03-05T22:37:00.002-08:00

Question :Can you have more than one cursor open at any one time in a program?
Answer :Yes.

Is DECLARE CURSOR executable

2009-03-05T22:37:00.001-08:00

Question :Is DECLARE CURSOR executable?
Answer :No.

What happens when you say OPEN CURSOR

2009-03-05T22:36:00.000-08:00

Question :What happens when you say OPEN CURSOR?
Answer :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 row.

How do you specify and use a cursor in a COBOL program

2009-03-05T22:35:00.000-08:00

Question :How do you specify and use a cursor in a COBOL program?
Answer :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.

Where would you specify the DECLARE CURSOR statement

2009-03-05T22:34:00.000-08:00

Question :Where would you specify the DECLARE CURSOR statement?
Answer :See answer to next question.

How would you retrieve rows from a DB2 table in embedded SQL

2009-03-05T22:26:00.002-08:00

Question :How would you retrieve rows from a DB2 table in embedded SQL? ?
Answer :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.

What is a cursor? why should it be used

2009-03-05T22:26:00.001-08:00

Question :What is a cursor? why should it be used?
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.

Why SELECT * is not preferred in embedded SQL programs

2009-03-05T22:09:00.000-08:00

Question :Why SELECT * is not preferred in embedded SQL programs?
Answer :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 over head. 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.

Consider the employee table with column PROJECT nullable. How can you get a list of employees who are not assigned to any project

2009-03-05T22:08:00.000-08:00

Question :Consider the employee table with column PROJECT nullable. How can you get a list of employees who are not assigned to any project?
Answer :SELECT EMPNO FROM EMP WHERE PROJECT IS NULL;

What do you accomplish by GROUP BY ... HAVING clause

2009-03-05T22:07:00.002-08:00

Question :What do you accomplish by GROUP BY ... HAVING clause?
Answer :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

When do you use a LIKE statement

2009-03-05T22:07:00.001-08:00

Question :When do you use a LIKE statement?
Answer :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.

What is 'LIKE' used for in WHERE clause? What are the wildcard characters

2009-03-05T22:06:00.000-08:00

Question :What is 'LIKE' used for in WHERE clause? What are the wildcard characters?
Answer :LIKE is used for partial string matches. ?%? ( for a string of any character ) and ?_? (for any single character ) are the two wild card characters.

Is BETWEEN inclusive of the range values specified

2009-03-05T22:04:00.000-08:00

Question :Is BETWEEN inclusive of the range values specified?
Answer :Yes.

In the WHERE clause what is BETWEEN and IN

2009-03-05T22:03:00.002-08:00

Question :In the WHERE clause what is BETWEEN and IN?
Answer :BETWEEN supplies a range of values while IN supplies a list of values.

What is the restriction on using UNION in embedded SQL

2009-03-05T22:03:00.001-08:00

Question :What is the restriction on using UNION in embedded SQL?
Answer :It has to be in a CURSOR.

What is UNION,UNION ALL

2009-03-05T22:02:00.000-08:00

Question :What is UNION,UNION ALL?
Answer :UNION : eliminates duplicates UNION ALL: retains duplicates Both these are used to combine the results of different SELECT statements. Suppose I have five SQL SELECT statements connected by UNION/UNION ALL, how many times should I specify UNION to eliminate the duplicate rows? - Once.

What is the use of VALUE function

2009-03-05T22:01:00.000-08:00

Question :What is the use of VALUE function?
Answer :1. Avoid -ve SQLCODEs by handling nulls and zeroes in computations 2. Substitute a numeric value for any nulls used in computation

How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a complete name

2009-03-05T22:00:00.000-08:00

Question :How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a complete name?
Answer :SELECT FIRSTNAME ? ? LASTNAME FROM EMP;

How do you retrieve the first 5 characters of FIRSTNAME column of EMP table

2009-03-05T21:59:00.000-08:00

Question :How do you retrieve the first 5 characters of FIRSTNAME column of EMP table?
Answer :SELECT SUBSTR(FIRSTNAME,1,5) FROM EMP;

My SQL statement SELECT AVG(SALARY) FROM EMP yields inaccurate results. Why

2009-03-05T21:58:00.000-08:00

Question :My SQL statement SELECT AVG(SALARY) FROM EMP yields inaccurate results. Why?
Answer :Because SALARY is not declared to have NULLs and the employees for whom the salary is not known are also counted.

Can you use MAX on a CHAR column

2009-03-05T21:57:00.000-08:00

Question :Can you use MAX on a CHAR column?
Answer :YES.

How do you find the maximum value in a column

2009-03-05T21:56:00.000-08:00

Question :How do you find the maximum value in a column?
Answer :Use SELECT MAX(...

What are aggregate functions

2009-03-05T21:54:00.000-08:00

Question :What are aggregate functions?
Answer :Bulit-in mathematical functions for use in SELECT clause.

How do you select a row using indexes

2009-03-05T21:48:00.000-08:00

Question :How do you select a row using indexes?
Answer :Specify the indexed columns in the WHERE clause.

How do you eliminate duplicate values in SELECT

2009-03-05T21:47:00.001-08:00

Question :How do you eliminate duplicate values in SELECT?
Answer :Use SELECT DISTINCT ...

How would you find out the total number of rows in a table

2009-03-05T21:44:00.000-08:00

Question :How would you find out the total number of rows in a table?
Answer :Use SELECT COUNT(*) ...