mysql的check约束问题

mysql手册中写道：存储引擎会解析check子句，但是会把它忽略掉

The CHECK clause is parsed but ignored by all storage engines.

现在还没找到check约束开启的东西，但找到了解决办法：

mysql> delimiter //
mysql> CREATE TRIGGER trig_sd_check BEFORE INSERT ON Customer
    -> FOR EACH ROW
    -> BEGIN
    -> IF NEW.SD<0 THEN
    -> SET NEW.SD=0;
    -> END IF;
    -> END
    -> //
mysql> delimiter ;

http://stackoverflow.com/questions/2115497/check-constraint-in-mysql-is-not-working