Interview Questions: Oracle, PL SQL

• What are the different types of joins?
• What is the difference between procedure and function
• What is group by function
• What is the difference between a where clause and having clause
• What are indexes. Advantages of indexes
• Triggers, how many triggers are available
• What does “i” represent in Oracle8i / 9i
• Difference between primary key and foreign key
• Can we have null in a primary key
• Can we have null in a foreign key, if yes , how many in a table
• What are cursors
• Give example of how SQL tuning can be done
• What is normalization
• Difference between delete and truncate
• Are you aware of water level mark in oracle database? What is it?
• What are views, snapshots and synonyms?
• What value one gets for “Select * from dual”
• Have you used Decode function? Give an example
• Example when inner joins was used?
• Example when outer joins was used?
• Datatypes supported by Oracle
• Can you explain how do index retrieve records from database
• What is commit and rollback
• What is the difference between these 2 queries
• Select count(*) from table
•Select count(1) from table
• Difference between NODATAFOUND and %NOFOUND
• Difference between IN and EXISTS? Which is faster in execution?
• What is referential integrity
• What are constraints
• What are transaction isolation levels?
• What are materialized views?

Database : Oracle, SQL, PL / SQL Technical Interview Questions

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?

SQL / PL SQL Questions

How do you convert a date to a string?
What is an aggregate function?
What is the dual table?
What are cursors? Distinguish between implicit and explict cursors?
Explain how cursors are used by Oracle?
What is PL/SQL? Describe the block structure of PL/SQL?
What is a nested subquery?
What are the various types of queries ?
Which of the following is not a schema object : Index, table, public synonym, trigger and package ?
What is dynamic sql in oracle?
What is the difference between a package, procedure and function
What is the difference between delete, drop and truncating a table
How many triggers are supported in Oracle
Are you aware of FLASHBACK concept ? What is it?
Describe oracle’s logical and physical structure?
What is data dictionary
What is the use of control files
How would store XML data in table ? What data type would be used for the columns?
Difference between post and commit?
Difference between commit and rollback?
What are savepoints?
Difference between a View and Synonym
How would you fetch system date from oracle
What is the difference between primary key, unique key, foreign key?
What is the difference between NO DATA FOUND and %NOTFOUND
What is cursor for loop
What are cursor attributes
What will you use in Query : IN or EXISTS? Why
Explain the difference between a data block, an extent and a segment.
What's the difference between logical and physical I/O?
What is an anonymous block?
What is a PL/SQL collection?
How can you tell if an UPDATE updated no rows?
How can you tell if a SELECT returned no rows?

Oracle DBA Questions and Answers

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