MySQL - TRIGGERS STOCK

    // TRIGGERS STOCK
    create database ventas
    go
    use ventas


    go
    CREATE TABLE articulo
        (  idArticulo int primary key,
        nombre varchar (100),
        stock int 
        )
    go
    create trigger trNoStockNegativo on articulo for insert, update
    as
        declare @texto varchar(300)
        if ( select stock from inserted ) < 0 
        begin
            set @texto = 'El stock del "'+(select nombre from inserted)+'" no puede quedar negativo'
            raiserror (@texto,16,1)
            rollback transaction
        end
    go

    create table venta
    (
    idventa int identity primary key,
    idArticulo int references articulo(idArticulo),
    cantidad int constraint "Tiene que vender algo" check (cantidad >0)
    )
    go
    insert into articulo values ( 1,'Platano',10)
    insert into articulo values ( 2,'Manzana',7)
    insert into articulo values ( 3,'Pera',2)

    go
    create trigger trNuevaVenta on venta for insert
    as
    declare @idArticuloVendido int
    declare @cantidad int

    set @idArticuloVendido =(select idArticulo from INSERTED) 
    set @cantidad =(select cantidad from INSERTED)

    update articulo set stock = stock - @cantidad where idArticulo = @idArticuloVendido

    go

    create trigger trBorrarventa on venta for delete 
    as
    declare @idArticuloVendido int
    declare @cantidad int
    
    set @idArticuloVendido =(select idArticulo from DELETED)
    set @cantidad =(select cantidad from DELETED)

    update articulo set stock = stock + @cantidad where idArticulo =@idArticuloVendido
    go

    //-- modificar !!
    create trigger trModificarVenta on venta for update
    as
    //-- eliminar venta anterior
    declare @idArticuloVendido int
    declare @cantidad int
    
    set @idArticuloVendido =(select idArticulo from DELETED)
    set @cantidad =(select cantidad from DELETED)

    update articulo set stock = stock + @cantidad where idArticulo =@idArticuloVendido

    //-- venta nueva

    set @idArticuloVendido =(select idArticulo from INSERTED) 
    set @cantidad =(select cantidad from INSERTED)

    update articulo set stock = stock - @cantidad where idArticulo = @idArticuloVendido

    go

    //-- todo en uno
    create trigger trMantenerStock on venta for update,delete,insert
    as

    update articulo set stock = stock +(select cantidad from DELETED) 
                            where idArticulo =(select idArticulo from DELETED)
    update articulo set stock = stock -(select cantidad from INSERTED)
                            where idArticulo = (select idArticulo from INSERTED)