CODEWITHSUNDEEP
mysqloracle-databasedatabase
lovespring
lovespring

Reputation: 19589

about foreign key constraints in mysql or other DBMS

such as this constraint:

alter table TABLE_NAME 
      add constraint FK_CONSTRAINT_ID foreign key (COLUMN_NAME)
      references PARENT_TABLE_NAME(PARENT_COLUMN_NAME) 
      on delete set null 
      on update set null;

will mysql do constraints check immediately (that is, check all rows) after add action

OR just later ON DELETE or ON UPDATE event?

How about other database?

If not immediatelly, how to do a mannually full table row check ?

Upvotes: 0

Views: 47

Answers (1)

Gordon Linoff
Gordon Linoff

Reputation: 1271231

A foreign key constraint is a property of a table and one or more columns in the table. It says that these columns refer to primary key (or unique indexed) columns in another table.

Hence, when the constraint is created, the table is checked to be sure that the constraint is valid.

The on delete and on update after what happens during those operations. It does not change the fact that the constraint is on the table and must be valid.

Upvotes: 2

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