Answer Posted / nitesh
It is mainly used in referential integrity constraints.
When you use primary key/candidate key of one relation(say,
r1) as foreign key in other relation(say, r2), you want
changes made to primary key/candidate key of r1 must reflect
in foreign key of r2. And this can be achieved by CASCADE
constraint.
eg. consider two relations account, branch(with primary key
branch_name)
create table account(.....
foreign key branch_name references branch
on delete cascade
on update cascade
..........)
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