Дополнение строки до заданной длины с обоих краев в MySQL

DROP FUNCTION IF EXISTS STRING_PAD_BOTH;

DELIMITER $$

CREATE FUNCTION STRING_PAD_BOTH(string TEXT, padLength INT, padString TEXT)
RETURNS TEXT
DETERMINISTIC
BEGIN
	DECLARE result TEXT DEFAULT NULL;
	IF (padLength = 0) THEN SET result = '';
	ELSEIF (padLength > 0) THEN
		BEGIN
			DECLARE padLengthDiff INT DEFAULT 0;
			SET padLengthDiff = padLength - CHAR_LENGTH(string);
			IF (padLengthDiff = 0) THEN SET result = string;
			ELSEIF (padLengthDiff > 0) THEN
				BEGIN
					DECLARE padLengthLeft INT DEFAULT 0;
					DECLARE padLengthRight INT DEFAULT 0;
					DECLARE padStringLength INT DEFAULT 0;
					SET padLengthLeft = FLOOR(padLengthDiff / 2);
					SET padLengthRight = padLengthDiff - padLengthLeft;
					SET padStringLength = CHAR_LENGTH(padString);
					SET result = CONCAT(
						SUBSTRING(REPEAT(padString, CEIL(padLengthLeft / padStringLength)), 1, padLengthLeft),
						string,
						SUBSTRING(REPEAT(padString, CEIL(padLengthRight / padStringLength)), 1, padLengthRight)
					);
				END;
			ELSE SET result = SUBSTRING(string, 1, padLength);
			END IF;
		END;
	END IF;
	RETURN result;
END$$

DELIMITER ;