MySQL basic three triggers

Product List--Table "goods" DDL:

CREATE TABLE goods (
gidInt (one) is not NULL,
namevarchar (DEFAULT) NULL,
numsmallint (6) DEFAULT NULL,
PRIMARY KEY ( gid )
) Engine=innodb DEFAULT Charset=utf8;

Order table -table "orders" DDL:

CREATE TABLE orders (
oidInt (one) is not NULL,
gidInt (one) DEFAULT NULL,
muchsmallint (6) DEFAULT NULL,
PRIMARY KEY ( oid )
) Engine=innodb DEFAULT Charset=utf8;

One, insert trigger:

Demand: When a customer buys a product, the inventory quantity of the item is automatically reduced.

Create trigger Trigerinsertorder after insert on orders for each row

Begin

Update goods set Num=num-new.much where Gid=new.gid;

End

Note: New represents a new row for the Orders table.

Second, delete trigger:

Requirements: After the customer cancels the order, the inventory quantity of the commodity table increases automatically.

Create trigger Triggerdeleteorder after delete on orders for each row

Begin

Update goods set Num=num+old.much where Gid=old.gid

End

Note: Old indicates that the Orders table deletes rows.

MySQL basic three triggers