Checking if a column has a certain value, then restrict another by a list

Question

I am wondering if there is any way for me to check if a column has a value, if the value is XXXXX then another column must be in the list of (A,B,C). something like:

CREATE TABLE test (a CHAR(60),b CHAR(60),Check (IF a == 'test' THEN b in ('a','b','c')));

Answer 1

In other words, in test rows, b must be in the list, while in non-test rows, b can be anything.

So for the check to succeed, b must be in the list, or the row must not be a test row:

CHECK (a <> 'test' OR b IN ('a', 'b', 'c'))

Mathematically, a → b is the same as ¬a ∨ b.