Listed here are Interview Questions for Database Interviews.
This mainly lists Oracle, SQL, PL SQL frequently asked questions in technical Interviews
1. What is DDL, DML ? How are they different?
2. What are different types of joins in SQL?
3. How do you select unique rows using SQL?
4. What is the difference between DELETE and TRUNCATE ?
5. What is the difference between a "where" clause and a "having" clause?
6. What is the difference between "procedure" and "function"?
7. What is the difference between "translate" and "replace" ?
8. How to remove duplicate records from a table?
9. What is a "trigger"?
10.What is the difference between "translate" and "replace"?
11.What is a VIEW?
12.What is the difference among "dropping a table", "truncating a table"
and "deleting all records" from a table
13.Explain new feature of 9i Database ? Explain new feature of 10g Database ?
14.How to use DECODE function?
15.What is “Group by” clause?
16.What are cursors and what are the situations you will use them?
17.What default packages are provided by Oracle?
18.How do you debug a oracle procedure /function?
19.How many triggers are available?
20.How are procedures executed?
Thursday, 3 January 2008
Oracle, SQL, PL / SQL Technical Interview Questions
Oracle SQL, PL/SQL Interview Question List
These are some Oracle SQL, PL/SQL Interview Question List
1. How do you convert a date to a string?
2. What is an aggregate function?
3. What is the dual table?
4. What are cursors? Distinguish between implicit and explict cursors?
5. Explain how cursors are used by Oracle?
6. What is PL/SQL? Describe the block structure of PL/SQL?
7. What is a nested subquery?
8. What are the various types of queries ?
9. Which of the following is not a schema object : Index, table, public synonym, trigger and package ?
10. What is dynamic sql in oracle?
11. What is the difference between a package, procedure and function?
12. What is the difference between delete, drop and truncating a table?
13. How many triggers are supported in Oracle
14. Are you aware of FLASHBACK concept ? What is it?
15. Describe oracle’s logical and physical structure?
16. What is data dictionary ?
17. What is the use of control files ?
18. How would store XML data in table ? What data type would be used for the columns?
19. Difference between post and commit?
20. Difference between commit and rollback?
21. What are savepoints?
22. What is the Difference between a View and Synonym?
23. How would you fetch system date from oracle?
24. What is the difference between primary key, unique key, foreign key?
25. What is the difference between NO DATA FOUND and %NOTFOUND?
26. What is cursor for loop?
27. What are cursor attributes?
28. What will you use in Query : IN or EXISTS? Why?
29. Explain the difference between a data block, an extent and a segment.?
30. What's the difference between logical and physical I/O?
31. What is an anonymous block?
32. What is a PL/SQL collection?
33. How can you tell if an UPDATE updated no rows?
34. How can you tell if a SELECT returned no rows?
The Difference Between %TYPE and %ROWTYPE
%TYPE and %ROWTYPE are used to define variables in PL/SQL as it is defined within the database. If the datatype or precision of a column changes, the program automically picks up the new definition from the database without having to make any code changes.
The %TYPE and %ROWTYPE constructs provide data independence, reduces maintenance costs, and allows programs to adapt as the database changes to meet new business needs.
%TYPE is used to declare a field with the same type as that of a specified table's column. Example:
DECLARE
v_EmpName emp.ename%TYPE;
BEGIN
SELECT ename INTO v_EmpName FROM emp WHERE ROWNUM = 1;
DBMS_OUTPUT.PUT_LINE('Name = ' || v_EmpName);
END;
/
%ROWTYPE is used to declare a record with the same types as found in the specified database table, view or cursor. Examples:
DECLARE
v_emp emp%ROWTYPE;
BEGIN
v_emp.empno := 10;
v_emp.ename := 'XXXXXXX';
END;
/
DECLARE
v_EmpRecord emp%ROWTYPE;
BEGIN
SELECT * INTO v_EmpRecord FROM emp WHERE ROWNUM = 1;
DBMS_OUTPUT.PUT_LINE('Name = ' || v_EmpRecord.ename);
DBMS_OUTPUT.PUT_LINE('Salary = ' || v_EmpRecord.sal);
END;
/
Oracle DBA Interview Questions
Here are Oracle DBA Questions and Answers in Interview (don't expect too much on this)
1. Explain database instance ?
A database instance (server) is a set of memory structures and background processes that access a set of database files.
The memory structures are used to store most queried data from database. This helps us to improve database performance by decreasing the amount of I/O performed against data file.
The process can be shared by all users.
2. What is parallel server?
Multiple instances accessing the same database (Only in Multi-CPU environments).
3. What is Schema ?
The set of objects owned by user account is called the schema
4. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table.An index is automatically created when a unique or primary key constraint clause is specified in create table command
5. What is a clusters? Explain
Group of tables physically stored together because they share common columns and are often used together is called Clusters.
6. What is a cluster key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stores only once for multiple tables in the cluster.
7. What are the basic element of an oracle Database ?
It consists ofone or more data filesone or more control filestwo or more redo log files
The database containsMultiple users/schemasone or more rollback segmentsone or more tablespacesData dictionary tables
User objects (tables,indexes,views etc)
The server that access the database consists of
SGA (Database buffer, Dictionary Cache Buffers, redo log buffers,Shared SQL pool)
SMON
PMON
LGWR
DBWR
ARCH
CKPT
RECO
Dispatcher
User process with associated PGA
8. What is deadlock ? Explain.
Two processes waiting to update the rows of a table which are locked by the other process then deadlock arises.
In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.
9. What is SGA ?
The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information about the database.
10. What is Shared SQL pool ?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
11. What is meant by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User process.
12. What is a data segment ?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.
13. What are the factors causing the reparsing of SQL statements in SGA ?
Due to insufficient Shared SQL pool size
Wednesday, 2 January 2008
Oracle 10g UTL_COMPRESS
Oracle 10g includes many PL/SQL enhancements including: utl_compress
The UTL_COMPRESS package provides an API to allow compression and decompression of binary data (RAW, BLOB and BFILE). It uses the Lempel-Ziv compression algorithm which is equivalent to functionality of the gzip utility. A simple example of it's usage would be:
SET SERVEROUTPUT ON
DECLARE
l_original_blob BLOB;
l_compressed_blob BLOB;
l_uncompressed_blob BLOB;
BEGIN
-- Initialize both BLOBs to something.
l_original_blob := TO_BLOB(UTL_RAW.CAST_TO_RAW('1234567890123456789012345678901234567890'));
l_compressed_blob := TO_BLOB('1');
l_uncompressed_blob := TO_BLOB('1');
-- Compress the data.
UTL_COMPRESS.lz_compress (src => l_original_blob,
dst => l_compressed_blob);
-- Uncompress the data.
UTL_COMPRESS.lz_uncompress (src => l_compressed_blob,
dst => l_uncompressed_blob);
-- Display lengths.
DBMS_OUTPUT.put_line('Original Length : ' || LENGTH(l_original_blob));
DBMS_OUTPUT.put_line('Compressed Length : ' || LENGTH(l_compressed_blob));
DBMS_OUTPUT.put_line('Uncompressed Length: ' || LENGTH(l_uncompressed_blob));
-- Free temporary BLOBs.
DBMS_LOB.FREETEMPORARY(l_original_blob);
DBMS_LOB.FREETEMPORARY(l_compressed_blob);
DBMS_LOB.FREETEMPORARY(l_uncompressed_blob);
END;
/
Tuesday, 1 January 2008
Oracle DBA : Backup on Tape Drive
For oracle DBA, here are some cases on Tape Drive Backup:
You want to take backup on tape drive but rman always store the backup on a default location
- how can we take backup on tape drive, should we have to install any extra softwares for tape drive or rman handle it itself?
You need thrid party Media managment software like veritas ,omnibackup,tivoli for backing up to tape.If you don't already have Media Management software, you can consider Oracle Secure Backup as a free alternative (assuming you are backing up one server to one tape drive). - how can we set the tape drive as our default location for backup?
how can we take backup on specified location e.g. d:\backup and how can we set this location as default location for backup?
To set the tape drive as the default, see Configuring the Default Device Type for Backups.
If you want the tape drive to be the default backup location, then you'll have to allocate a disk channel to produce backups to d:\backup. You can configure the disk format as CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT 'd:\backups'; and then allocate a disk channel during backup (Manually Overriding Configured Channels).
