Create a check constraint that a value exists in another table

Question

I'm using a mariaDB instance and I would like to create a check constraint that a value must exist in another table. In the below example, TableA.Number must already exist in TableB.

TableA

Name varchar(30)

Number int

TableB

Number int

Answer 1

I don't know if I understand your question correctly, but have you already tried with foreign keys?

https://mariadb.com/kb/en/foreign-keys/

Answer 2

You can create a trigger to achieve the same

CREATE TRIGGER Check_exist_in_B BEFORE

INSERT ON TableA >

DECLARE ExistingNum INT;>

SET @ExistingNum : = (
        SELECT NUMBER
        FROM TableB
        WHERE b.number = new.number
        ) >

IF (@ExistingNum IS NULL) THEN > SIGNAL SQLSTATE '45000' >
    SET MESSAGE_TEXT = 'Not exists in B' >
    END;