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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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