Friday, 6 February 2015

Most Recently PLSQL Interview Questions and Answers

Below are some important PLSQL interview questions which are asked in most MNC company interviews for beginners or professionals.
11. Give two examples of referential integrity constraints. | PL/SQL Questions
A primary key and a foreign key.

12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables? | PL/SQL Questions
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.

13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each. | PL/SQL Questions
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.

14. What command would you use to create a backup control file? | PL/SQL Questions
Alter database backup control file to trace.

15. Give the stages of instance startup to a usable state where normal users may access it. | PL/SQL Questions
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened

16. What column differentiates the V$ views to the GV$ views and how? | PL/SQL Questions
The INST_ID column which indicates the instance in a RAC environment the information came from.

17. How would you go about generating an EXPLAIN plan? | PL/SQL Questions
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql

18. How would you go about increasing the buffer cache hit ratio? | PL/SQL Questions
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.

19. Explain an ORA-01555. | PL/SQL Questions
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.

20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE. | PL/SQL Questions
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
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