The PRIMARY KEY constraint uniquely identifies each record in a database table.Primary keys must contain unique values.A primary key column not contain NULL values.Each table should have a primary key
On 2014-06-06 06:10:49.0
sujata
Its mainly used for DB operation..In one table only one PK l be allowed,it l not allow duplicate value.
On 2014-06-06 06:10:49.0
subha064
point should be noted => We can use combination of more than one column as a primary key.
On 2014-06-06 06:16:36.0
hablu
can u exaplin @hablu?
On 2014-06-06 06:21:37.0
subha064
that is called Composite primary key.
On 2014-06-06 06:22:49.0
subha064
@subha Ya correct that is composite primary key.
On 2014-06-06 06:41:30.0
hablu
the constraint that allow for column should be unique and not null.there wii be only one PK in a table.