Check restriction for mysql

Mysql does not suppot for check restriction but oracle does. Here using trigger we can achive the same restrction as check does.

Scenario:

Here is a IDcard field in table student with a restriction that the length of IDCrad must less than 18.

4 parameters we can use:

1. trigger-name: credit_tri

2. target-table:student

3. target-field:IDCard

4. error-msg:"length is above 18,cannot insert"

mysql> delimiter $mysql> create trigger credit_tri before insert     -> on student for each row    -> begin    ->     declare msg varchar(200);     ->     if (new.IDCard > 18) then      ->         set msg = "length is above 18. Cannot insert.";        ->             signal sqlstate 'HY000' SET message_text = msg;        ->     end if;    -> end $