The rule of thumb is to use CHECK
constraint when possible.
A CHECK
constraint is faster, simpler, more portable, needs less code and is less error prone. Triggers can easily be circumvented by other triggers, for instance.
A TRIGGER
is more complicated. Use it when you have to, for more complex requirements.
If a CHECK
constraint is too restrictive for your case or causes trouble reloading a dump, you could use the NOT VALID
modifier as middle ground (Postgres 9.2+). And, optionally, VALIDATE
it later. See: