Using variable for error code in MySQL with SQLSTATE - mysql

Question

I'm trying to manage my own errors in MySQL using a procedure and an error message table named "error_messages".
How can I manage to select a specific error message in that table?
I would like to do something like this.
DELIMITER $$
CREATE PROCEDURE throw_error_test (divisor INT)
BEGIN
SET #errorCode = '45123';
IF divisor = 0 THEN
SIGNAL SQLSTATE #errorCode
SET MESSAGE_TEXT = SELECT message
FROM error_messages
WHERE id = #errorCode;
END IF;
END;
Thanks for helping

Answer 1

As documented under SIGNAL Syntax:
The condition_value in a SIGNAL statement indicates the error value to be returned. It can be an SQLSTATE value (a 5-character string literal) or a condition_name that refers to a named condition previously defined with DECLARE ... CONDITION (see Section 13.6.7.1, “DECLARE ... CONDITION Syntax”).
[ deletia ]
Valid simple_value_specification designators can be specified using stored procedure or function parameters, stored program local variables declared with DECLARE, user-defined variables, system variables, or literals.
Therefore, for the MESSAGE_TEXT you could use a user variable—but my preference would be for stored program local variables; however can't specify the SQLSTATE with a variable:
CREATE PROCEDURE throw_error_test (divisor INT)
BEGIN
DECLARE _messageText VARCHAR(128);
IF divisor = 0 THEN
SELECT message
INTO _messageText
FROM error_messages
WHERE id = '45123';
SIGNAL SQLSTATE '45123' SET MESSAGE_TEXT = _messageText
END IF;
END
For the avoidance of doubt, the underscore _ prefixes are purely a convention that I adopt to avoid ambiguity—they are not a necessary part of a local variable name.