Friday, October 28, 2011
ORACLE SQL TUTORIAL: DEFERRABLE CONSTRAINTS
DEFERRABLE
CONSTRAINTS
Each
constraint has two additional attributes to support deferred checking of
constraints.
Ø Deferred initially immediate
Ø Deferred initially deferred
Deferred
initially immediate checks for constraint violation at the time of insert.
Deferred
initially deferred checks for constraint violation at the time of commit.
Ex:
SQL>
create table student(no number(2), name varchar(10), marks number(3),
constraint
un unique(no) deferred initially
immediate);
SQL> create table student(no number(2),
name varchar(10), marks number(3), constraint
un unique(no) deferred initially
deferred);
SQL> alter table student add constraint
un unique(no) deferrable initially deferred;
SQL> set constraints all immediate;
This will enable all the constraints
violations at the time of inserting.
SQL> set constraints all deferred;
This
will enable all the constraints violations at the time of commit.
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