Mysql Trigger multiple stat - mysql

Question

I have 3 Tables : Venta , Factura, Producto . So I'm trying to create a Trigeer that insert values on table "Factura" and udpate a value on "Producto" when inserting on Venta. This is my first Trigger and I'dont know what I'm doing wrong, I think maybe I'm not getting the idea on how to declare variables ?. I'll appreciate any light on this .
I've modified the code as I did understand. Now I'm getting a syntax error on the line were de UPDATE instruction is. By the way, the tables are:
mysql> describe Producto;
+------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+-------+
| Cod_Prod | varchar(8) | NO | PRI | NULL | |
| Nom_Prod_P | varchar(16) | NO | | NULL | |
| Precio_P | decimal(9,2) | NO | | NULL | |
| Cantidad_P | int(6) | NO | | NULL | |
+------------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> describe Venta;
+--------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| id_Venta | varchar(9) | NO | PRI | NULL | |
| Fecha_V | date | NO | | NULL | |
| Nom_Cli_V | varchar(24) | NO | | NULL | |
| Rut_Cli_V | varchar(12) | NO | | NULL | |
| Dir_Cli_V | varchar(16) | NO | | NULL | |
| Nom_Prod_V | varchar(16) | NO | | NULL | |
| Precio_V | decimal(9,2) | NO | | NULL | |
| Cant_Prod_V | int(6) | NO | | NULL | |
| Forma_Pago_V | varchar(12) | NO | | NULL | |
+--------------+--------------+------+-----+---------+-------+
9 rows in set (0.00 sec)
mysql> describe Factura;
+--------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+----------------+
| Num_Fac | int(11) | NO | PRI | NULL | auto_increment |
| Fecha_F | date | NO | | NULL | |
| Nom_Cli_F | varchar(24) | NO | | NULL | |
| Rut_Cli_F | varchar(12) | NO | | NULL | |
| Dir_Cli_F | varchar(16) | NO | | NULL | |
| Nom_Prod_F | varchar(24) | NO | | NULL | |
| Cant_Prod_F | int(6) | NO | | NULL | |
| Neto | decimal(9,2) | NO | | NULL | |
| IVA | decimal(9,2) | NO | | NULL | |
| Total | decimal(9,2) | NO | | NULL | |
| Forma_Pago_F | varchar(12) | NO | | NULL | |
+--------------+--------------+------+-----+---------+----------------+
11 rows in set (0.00 sec)
DELIMITER $$
CREATE TRIGGER Genera_Factura_Before
BEFORE INSERT
ON TuOficina.Venta
FOR EACH ROW
BEGIN
DECLARE calc_iva decimal(9,2);
DECLARE calc_neto decimal(9,2);
DECLARE gran_total decimal(9,2);
DECLARE prod_descuento int(6);
SET calc_neto = new.Precio_V * new.Cant_Prod_V;
SET calc_iva = calc_neto / 0.19;
SET gran_total = calc_neto + calc_iva;
SET prod_descuento = new.Cant_Prod_V - Cantidad_P;
INSERT INTO Factura(Fecha_F, Nom_Cli_F, Rut_Cli_F, Dir_Cli_F, Nom_Prod_F, Cant_Prod_F, Neto, IVA, Total, Forma_Pago_F) VALUES (Fecha_V, new.Nom_Cli_V, new.Rut_Cli_V, new.Dir_Cli_V, new.Nom_Prod_V, new.Cant_Prod_V, calc_neto, calc_iva, gran_total, new.Forma_Pago_V);
UPDATE Producto SET Cantidad_P = prod_descuento WHERE Nom_Prod_P = new.Nom_Prod_P;
END$$

Answer 1

A couple of issues stand out immediately...
In MySQL numeric literal, the decimal point character must be a period (dot) not a comma.
SET iva = neto / 0,19 ;
^
In an INSERT trigger, there is no OLD. value for a column in the table. That is valid only in an UPDATE or DELETE trigger.
SET prod_descuento = new.Cant_Prod_V - old.Cant_Prod_P;
^^^^
Also, beware of columns and variables with the same name, in the context of a SQL statement. When its possible a reference could be to a variable or a column, MySQL will resolve the reference to be to the column.