Question

I have a table with 2 columns (A as bool and B as text), these columns can be:

1. both are null
2. if A is False, then B should be null
3. if A is True, then B should be not null

There are rules. I want to create a stored procedure or function to check these rules when row adding or updating (via trigger). What is better, stored procedure or function? If function, which type? In general, which variant is the best (return boolean or other way etc)?

Answer 1

I think you’re after a CHECK Constraint.

Example:

ALTER TABLE Xxx
  ADD CONSTRAINT chk_Xxx 
  CHECK ( (A IS NULL AND B IS NULL) 
       OR (A = 0 AND B IS NULL) 
       OR (A = 1 AND B IS NOT NULL)
        ) ;