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Monday, June 17, 2019

55 Top PL/SQL Interview Questions and Answers {Updated}

PL/SQL Interview Questions and Answers for experienced PDF, Read commonly asked PL/SQL Job Interview Questions with Answers PDF for Freshers.

Read PL/SQL Interview Questions and Answers

Name two files used for network connection to a database.

What is the difference between the SQL*Loader and IMPORT utilities?
These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.

How can you enable a trace for a session?

How can you gather statistics on a table?
The ANALYZE command.

You have just compiled a PL/SQL package but got errors, how would you view the errors?

Explain what partitioning is and what its benefit is.
Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.

How can you rebuild an index?

How would you determine who has added a row to a table?
Turn on fine grain auditing for the table.

What view would you use to determine free space in a tablespace?

What view would you use to look at the size of a data file?

How do you resize a data file?

How do you add a data file to a tablespace?

When creating a user, what permissions must you grant to allow them to connect to the database?
Grant CONNECT to the user.

Name a tablespace automatically created when you create a database.
The SYSTEM tablespace.

What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.

What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents.

Give two methods you could use to determine what DDL changes have been made.
You could use Log miner or Streams

How would you force a log switch?

Describe what redo logs are
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.

How would you determine what sessions are connected and what resources they are waiting for?

What background process refreshes materialized views?
The Job Queue Processes.

When a user process fails, what background process cleans up after it?

Explain materialized views and how they are used
Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.

Where in the Oracle directory tree structure are audit traces placed?
In Unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer

Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed Statistics

Explain the use of table functions.
Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.

Explain the difference between a FUNCTION, PROCEDURE, and PACKAGE
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package, on the other hand, is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.

What command would you use to encrypt a PL/SQL application?

Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.

How would you determine the time zone under which a database was operating?
select DBTIMEZONE from dual;

Explain the difference between $ORACLE_HOME and $ORACLE_BASE
ORACLE_BASE is the root directory for Oracle. ORACLE_HOME located beneath ORACLE_BASE is where the Oracle products reside.

Explain an ORA-01555.
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.

How would you go about increasing the buffer cache hit ratio?
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.

How would you go about generating an EXPLAIN plan?
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

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

Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT – Instance startup
STARTUP MOUNT – The database is mounted
STARTUP OPEN – The database is opened

What command would you use to create a backup control file?
Alter database backup control file to trace.

Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
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.

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?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.

Give two examples of referential integrity constraints.
A primary key and a foreign key.

What type of index should you use on a fact table?
A Bitmap index.

Give the two types of tables involved in producing a star schema and the type of data they hold
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.

Give the reasoning behind using an index
Faster access to data blocks in a table.

Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

Where would you look for errors from the database engine?
In the alert log.

Give two examples of how you might determine the structure of the table DEPT
Use the describe command or use the dbms_metadata.get_ddl package.

Explain the difference between a data block, an extent, and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.

How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.

You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text-based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.

Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.

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