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Oracle Interview Questions and Answers



What is the advantage of a stored procedure over a database trigger ?
We have control over the firing of a stored procedure but we have no control over the firing of a trigger.

What is the maximum no. of statements that can be specified in a trigger statement ?
One.

Can views be specified in a trigger statement ?
No

What are the values of :new and :old in Insert/Delete/Update Triggers ?
INSERT : new = new value, old = NULL
DELETE : new = NULL, old = old value
UPDATE : new = new value, old = old value

What are cascading triggers? What is the maximum no of cascading triggers at a time?
When a statement in a trigger body causes another trigger to be fired, the triggers are said to be cascading. Max = 32.

What are mutating triggers ?
A trigger giving a SELECT on the table on which the trigger is written.

What are constraining triggers ?
A trigger giving an Insert/Update on a table having referential integrity constraint on the triggering table.

Describe Oracle database's physical and logical structure ?
Physical : Data files, Redo Log files, Control file.
Logical : Tables, Views, Tablespaces, etc.

Can you increase the size of a tablespace ? How ?
Yes, by adding datafiles to it.

What is the use of Control files ?
Contains pointers to locations of various data files, redo log files, etc.

What is the use of Data Dictionary ?
Used by Oracle to store information about various physical and logical Oracle structures e.g. Tables, Tablespaces, datafiles, etc

What are the advantages of clusters ?
Access time reduced for joins.

What are the disadvantages of clusters ?
The time for Insert increases.

Can Long/Long RAW be clustered ?
No.

Can null keys be entered in cluster index, normal index ?
Yes.

Can Check constraint be used for self referential integrity ? How ?
Yes. In the CHECK condition for a column of a table, we can reference some other column of the same table and thus enforce self referential integrity.

What are the min. extents allocated to a rollback extent ?
Two

What are the states of a rollback segment ? What is the difference between partly available and needs recovery ?
The various states of a rollback segment are :
ONLINE, OFFLINE, PARTLY AVAILABLE, NEEDS RECOVERY and INVALID.

What is the difference between unique key and primary key ?
Unique key can be null; Primary key cannot be null.

An insert statement followed by a create table statement followed by rollback ? Will the rows be inserted ?
No.

an you define multiple savepoints ?
Yes.

Can you Rollback to any savepoint ?
Yes.

What is the maximum no. of columns a table can have ?
254.

What is the significance of the & and && operators in PL SQL ?
The & operator means that the PL SQL block requires user input for a variable. The && operator means that the value of this variable should be the same as inputted by the user previously for this same variable. If a transaction is very large, and the rollback segment is not able to hold the rollback information, then will the transaction span across different rollback segments or will it terminate ? It will terminate (Please check ).

Can you pass a parameter to a cursor ?
Explicit cursors can take parameters, as the example below shows. A cursor parameter can appear in a query wherever a constant can appear. CURSOR c1 (median IN NUMBER) IS SELECT job, ename FROM emp WHERE sal > median;

What are the various types of RollBack Segments ?
Public Available to all instances
Private Available to specific instance

Can you use %RowCount as a parameter to a cursor ?
Yes

Is the query below allowed :
Select sal, ename Into x From emp Where ename = 'KING'
(Where x is a record of Number(4) and Char(15))

Yes

Is the assignment given below allowed :
ABC = PQR (Where ABC and PQR are records)

Yes

Is this for loop allowed :
For x in &Start..&End Loop

Yes

How many rows will the following SQL return :
Select * from emp Where rownum < 10;

9 rows

How many rows will the following SQL return :
Select * from emp Where rownum = 10;

No rows

Which symbol preceeds the path to the table in the remote database ?
@

Are views automatically updated when base tables are updated ?
Yes

Can a trigger written for a view ?
No

If all the values from a cursor have been fetched and another fetch is issued, the output will be : error, last record or first record ?
Last Record

A table has the following data : [[5, Null, 10]]. What will the average function return ?
7.5

Is Sysdate a system variable or a system function?
System Function

Consider a sequence whose currval is 1 and gets incremented by 1 by using the nextval reference we get the next number 2. Suppose at this point we issue an rollback and again issue a nextval. What will the output be ?
3

Definition of relational DataBase by Dr. Codd (IBM)?
A Relational Database is a database where all data visible to the user is organized strictly as tables of data values and where all database operations work on these tables.

What is Multi Threaded Server (MTA) ?
In a Single Threaded Architecture (or a dedicated server configuration) the database manager creates a separate process for each database user. But in MTA the database manager can assign multiple users (multiple user processes) to a single dispatcher (server process), a controlling process that queues request for work thus reducing the databases memory requirement and resources.

Which are initial RDBMS, Hierarchical & N/w database ?
RDBMS - R system
Hierarchical - IMS
N/W - DBTG

What is Functional Dependency
Given a relation R, attribute Y of R is functionally dependent on attribute X of R if and only if each X-value has associated with it precisely one -Y value in R

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