What is the difference between DROP,DELETE,TRUNCATE table ?
Delete:It's an DML command which is used for deleting
particular table in the database...even though we delete the
data we can regain it by rollback command.

Example:SQL> SELECT COUNT(*) FROM emp;

  COUNT(*)
----------
        14

SQL> DELESQL> SELECT COUNT(*) FROM emp;

  COUNT(*)
----------
        14

SQL> DELETE FROM emp WHERE job = 'CLERK';

4 rows deleted.

SQL> COMMIT;

Commit complete.

Truncate:This command is a DDL Command which is used to
delete a table...I Just Conclude it as
Truncate=Delete+Commit...once u applied this on table u
can't get the data back...but the structure will be there..

Example:

SQL> TRUNCATE TABLE emp;

Table truncated.

SQL> SELECT COUNT(*) FROM emp;

  COUNT(*)
----------
         0

Drop:It is used to destroy entire structure of a
table...once we apply this command on any particular table
we can't get it in anyway...so be cautious while applying
this command.

Example:

SQL> DROP TABLE emp;

Table dropped.

SQL> SELECT * FROM emp;
SELECT * FROM emp
              *
ERROR at line 1:
ORA-00942: table or view does not exist

Select 10 rows from a table ?

  Answer : Use TOP keyword to select 10 rows from a table.

Can we have more then primary Key in table ?

  Answer : We can't use more than one Primary key in a  
           table because Primary key is Unique Value.

What is mean by NULL value ?NULL means "" or 0 or
undefined ?

   Answer : NULL means empty ie. ""

What are the grouping function in SQL ?

Grouping functions are: 
max()
min()
sum()
avg()

Select 10 rows from a table ?
select * from table_name where count(*) <=10
or

select top 10 from table _name

10. What is mean by NULL value ? NULL means "" or 0 or
undefined ?

Null is not equal to "" or 0. it is un identified value

12. Can we have more then primary Key in table ?
no, we can't.

2. If base table of a view deleted means, what will happen
while we querying on view ? will give any error ?

i dont know exactly. but it likely base table doesnt exists.

4. What is constraints and types ?
types:
primary key
foreign key
not null
unique
defaults
check
rule

10) Null is not equal to "" or 0. it is un identified value
means suppose there is column Phone number.
If we do not any phone number we can insert NULL.
"" means empty String.
Select * from table where roll=""(EMPTY)
select * from table where roll is NULL(UNDEFINED)

2) Correct Answer.
View is made up of base tables. Suppose we select data from 
two table table1 & table2 ,these are base tables.
He wants to ask u if we drop a table table2,Will view give 
error.
  Yes.But if we recreate the table we can query the view 
again.

Try it by urself--
First create the view by selecting the data from two tables 
then select columns from view
Suppose select * from view1
then drop one of the tables 
then select * from view1 gives error.


12) NO.


13) ENTITY INTEGRITY--We cannit insert null in  a parimary 
key. CZ if two columns have tha value we cannot distinguish 
b/w two rows.

REFERENTIAL INTEGRITY---Vales in foregn key table are only 
those that match a value in a primary key table.

DOMAIN CONSTRAINT--A unique value for a column.
Exampl--Empid

RollBack Mean Transaction is Rolled Back to That State me 
undo The Thing That we Have Done

Commit Mean Transaction is Commited to that state me the 
the thing we have done is save

SavePoint is Concept of ORacle mean
For A Long Transaction we have Declare save point 
intermediate so that the transction before savepoint is 
commited .