MySQL trigger insert after insert into another table - mysql

Question

I want to add a foreign key into tblprowareinventory whenever I insert into tblprowareproducts:
tblProwareproducts
CREATE TABLE `tblprowareproducts` (
`ItemID` int(11) NOT NULL,
`ItemCode` varchar(30) NOT NULL,
`itemDescription` varchar(60) NOT NULL,
`Strand` varchar(30) NOT NULL,
`UnitCost` double NOT NULL,
`SaleCost` double NOT NULL,
`CategoryID_fk` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
ALTER TABLE `tblprowareproducts`
ADD PRIMARY KEY (`ItemID`),
ADD KEY `CategoryID_fk` (`CategoryID_fk`);
ALTER TABLE `tblprowareproducts`
MODIFY `ItemID` int(11) NOT NULL AUTO_INCREMENT;
ALTER TABLE `tblprowareproducts`
ADD CONSTRAINT `tblprowareproducts_ibfk_1` FOREIGN KEY (`CategoryID_fk`) REFERENCES `tblprowarecategory` (`PCategoryID`) ON DELETE CASCADE ON UPDATE CASCADE;
COMMIT;
tblProwareinventory
CREATE TABLE `tblprowareinventory` (
`inventoryID` int(11) NOT NULL,
`ItemID_FK` int(11) NOT NULL,
`DateOfInventory` date NOT NULL,
`CurrentQuantity` int(11) NOT NULL,
`TotalQuantity` int(11) NOT NULL,
`DeliveredQuantity` int(11) NOT NULL,
`PhysicalCount` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
ALTER TABLE `tblprowareinventory`
ADD PRIMARY KEY (`inventoryID`),
ADD KEY `ItemID_FK` (`ItemID_FK`);
ALTER TABLE `tblprowareinventory`
ADD CONSTRAINT `tblprowareinventory_ibfk_2` FOREIGN KEY (`ItemID_FK`) REFERENCES `tblprowareproducts` (`ItemID`) ON DELETE CASCADE ON UPDATE CASCADE;
COMMIT;
INSERT INTO tblprowareinventory(ItemID_FK)
VALUES ((SELECT ItemID FROM tblprowareproducts))
but I get this error:

Answer 1

You can use the following CREATE TRIGGER statement:
DELIMITER //
CREATE DEFINER = `root`#`localhost` TRIGGER AddToInventory AFTER INSERT ON tblprowareproducts
FOR EACH ROW
BEGIN
INSERT INTO tblprowareinventory (ItemID_FK) VALUES (NEW.ItemID);
END;//
DELIMITER ;
Note: You have to remove your current trigger on phpMyAdmin or with the following statement: DROP TRIGGER AddToInventory; to successfully run this CREATE TRIGGER statement.
The TRIGGER successfully add a new row to the tblprowareinventory table with the NEW.ItemID, but you defined a PRIMARY KEY on the inventoryID of tblprowareinventory table. That's OK, but after trying INSERT a second row on tblprowareinventory table, you should get an error:
#1062 - Duplicate entry '0' for key 'PRIMARY'
The TRIGGER tries to INSERT a second row on tblprowareinventory table with 0 on the inventoryID column. This is not possible because 0 can only exists once on the inventoryID column.
You can solve this issue using a AUTO_INCREMENT on the inventoryID column too:
ALTER TABLE `tblprowareinventory` MODIFY `inventoryID` INT(11) NOT NULL AUTO_INCREMENT;
To INSERT a new row on tblprowareproducts table I used the following statement:
INSERT INTO `tblprowareproducts` (`ItemID`, `ItemCode`, `itemDescription`, `Strand`, `UnitCost`, `SaleCost`, `CategoryID_fk`)
VALUES (NULL, '111', '111', '111', '1', '1', '1')