What Is The Use Of CASCADE CONSTRAINT ?
cascading is used for maintaining referencial integrity rules, which says that foreign key attributes values should be either subset of primary key values or null.
with cascading when parent is deleted child could be deleted/set null/set default according to cascade type.All this is for maintaing integrity.
The cascade option of the drop clause causes any dependent constraints also to be dropped.
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.
What is the difference between TRUNCATE and DELETE command ?
TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back.
WHERE clause can be used with DELETE and not with TRUNCATE.
TRUNCATE resets the identity and DELETE does not .
If we use TRUNCATE command it will delete the physical structure of the table and retains the logical structure of same as for the next usage.
DELETE is used to delete a particular row from the table.
DELETE is used to delete a particular row from the table.
when we truncate a table then no trigger fired with associate table but in delete sts the trigger will be fire.
Truncate is fast and delete is not because delete have undo information .
