问题
I have inherited an application that uses MySQL and that is used by a PHP front end. The guy that wrote this system has gone to some fairly convoluted lengths to ensure that codes that users enter are valid - and tat means that these codes also exist in another table.
When I first saw this I wondered why he hadn't used CHECK constraints and let the dbms sort this out - I have visions of a load of different programs implementing the same checks instead of just the one place in the dbms. And then I found out that MySQL doesn't support Check constraints (not strictly true - it supports the syntax but just ignores it).
Is there a way that I can implement Check Constraints in MySQL?
Any hints, suggestions etc, would be great.
回答1:
You can implement something similar to them with triggers, but MySQL itself doesn't support CHECK constraints. Don't worry though, it'll let you define them and just silently ignore them!
来源：https://stackoverflow.com/questions/706231/mysql-and-check-constraints