SQL-cascading Delete and update (referential integrity)

Syntax:
Foreign key
(Column [,... n])
References referenced_table_name [(ref_column [,... n])]
[On Delete cascade]
[On update cascade]

Note:
Column: column name
Referenced_table_name: name of the primary key table referenced by the foreign key
Ref_name: primary key column of the Table to be referenced by the foreign key
On Delete: deletes a cascading.
On update: Update Cascade

 

 

Alter table B add constraint snum

Foreign key (snum) references a (snum) on update cascade, delete cascade;

Alter table c add constraint snum

Foreign key (snum) references a (snum) on Delete cascade, delete cascade;

// Then all records these contain snum = 1 will be deleted from table A, B and C.

Delete from a where snum = 1;

 

// Then all records these contain snum = 2 will be updated from Table A, B and C.

Update a set snum = 11 where snum = 2;