[jhanschoo]

Here's an example of a "complex" constraint. You have a restaurant reservation system, and reservations are stored as time intervals. Each restaurant has a capacity, and you need to ensure that a booking does not make it so that the restaurant exceeds capacity at any point of time.

One way to resolve it with triggers is to have a stored procedure fetch all the records that intersect the new booking's interval, and procedurally count the number of concurrent bookings at each record's start and end times; the constraint would be violated if and only if the count at any point plus the pax of the new booking exceeds capacity.

[zepolen]

Imho that's the only way. Anything else can end up in invalid state.