Throw an error in a MySQL trigger

Question

If I have a trigger before the update on a table, how can I throw an error that prevents the update on that table?

Answer 1

The following procedure is (on mysql5) a way to throw custom errors , and log them at the same time:

create table mysql_error_generator(error_field varchar(64) unique) engine INNODB;
DELIMITER $$
CREATE PROCEDURE throwCustomError(IN errorText VARCHAR(44))
BEGIN
    DECLARE errorWithDate varchar(64);
    select concat("[",DATE_FORMAT(now(),"%Y%m%d %T"),"] ", errorText) into errorWithDate;
    INSERT IGNORE INTO mysql_error_generator(error_field) VALUES (errorWithDate);
    INSERT INTO mysql_error_generator(error_field) VALUES (errorWithDate);
END;
$$
DELIMITER ;


call throwCustomError("Custom error message with log support.");