MySQL: Solve my MySQL Cursor Error:1064

Question

DROP TRIGGER IF EXISTS `ACTUALIZAR_LOTE_DETALLE`;
DELIMITER //
CREATE TRIGGER `ACTUALIZAR_LOTE_DETALLE` AFTER INSERT ON `detalle_envio`
FOR EACH ROW BEGIN 
DECLARE ID_INVENTARIO_IN INT;
DECLARE ID_LOTE_DETALLE_MIN INT;
DECLARE CANTIDAD_A_COMPARAR INT;
DECLARE CANTIDAD_A_RESTAR INT;
SET CANTIDAD_A_RESTAR = new.cantidad_enviado;
SET ID_INVENTARIO_IN = (Select id_inventario from detalle_requisicion WHERE id_detalle_requisicion = new.id_detalle_requisicion); 
DECLARE cur_id CURSOR FOR SELECT id_lote_detalle from lote_detalle WHERE id_inventario = ID_INVENTARIO_IN AND cantidad > 0;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET DONE = 1;
OPEN cur_id;    
read_loop: LOOP
FETCH cur_id INTO LOTE_DETALLE_IDS;
SET CANTIDAD_A_COMPARAR = select cantidad from lote_detalle where id_lote_detalle = LOTE_DETALLE_IDS;
IF CANTIDAD_A_RESTAR > CANTIDAD_A_COMPARAR THEN
UPDATE `lote_detalle` SET cantidad=cantidad-CANTIDAD_A_COMPARAR WHERE id_lote_detalle = LOTE_DETALLE_IDS;
SET CANTIDAD_A_RESTAR = CANTIDAD_A_RESTAR - CANTIDAD_A_COMPARAR;
ELSE
UPDATE `lote_detalle` SET cantidad=cantidad-CANTIDAD_A_RESTAR WHERE id_lote_detalle = LOTE_DETALLE_IDS;
LEAVE read_loop;
END IF;
IF DONE = 1 THEN
LEAVE read_loop;
END IF;
END LOOP read_loop;
CLOSE cur_id;
END
//
DELIMITER ;

Is anything in the cursor? the query or something? Is anything in the Syntax? Cause i have based this Trigger from the syntax of the MySQL Forums This is the Error:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE cur_id CURSOR FOR SELECT id_lote_detalle from lote_detalle WHERE id_inve' at line 9

Answer 1

There are at least following issues with your code:

1. All declarations should come before any statements (SET in your case). That's what is causing your immediate error.
2. You didn't declare DONE variable
3. You didn't declare LOTE_DETALLE_IDS variable, but you declared ID_LOTE_DETALLE_MIN which you didn't use. Perhaps you should rename ID_LOTE_DETALLE_MIN to LOTE_DETALLE_IDS then.
4. Since declarations go first you have to re-write your cursor definition (e.g. with subquery) because ID_INVENTARIO_IN variable isn't initialized yet

Your whole declaration section can be re-written in a following manner

-- declaration of variables of the same type can be combined
DECLARE ID_INVENTARIO_IN, 
        LOTE_DETALLE_IDS, 
        CANTIDAD_A_COMPARARINT, 
        CANTIDAD_A_RESTAR, 
        DONE INT;
DECLARE cur_id CURSOR FOR ...
DECLARE CONTINUE HANDLER ...

-- initialize variables
SET ...

Now, I believe your trigger most likely can be re-written with just update statement(s). You can get help with it if you explain in plain words what you're trying to achieve and provide exact table schemas and sample data.