MySQL Foreign key constraint - Error 1452 - Cannot add or update child row

Question

I've used the other posts on this topic, but I'm having no luck.

Here's the code I execute:

UPDATE tblOrderItems SET `ItemID` = 0004 WHERE `OrderNum`= 203 AND `OrderItemID` = 26

Here's my error:

Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`cai0066`.`tblOrderItems`, CONSTRAINT `ItemID` FOREIGN KEY (`ItemID`) REFERENCES `tblCatalogItems` (`ItemID`))

Notes:

1. It happens when I either INSERT or UPDATE into tblOrderItems.
2. tblCatalogItems does have an ItemID of 0004. See: this

Here are the create statements generated by MySQL Workbench:

delimiter $$

CREATE TABLE `tblCatalogItems` (
  `ItemID` varchar(10) NOT NULL DEFAULT '',
  `ItemName` varchar(50) DEFAULT NULL,
  `Wholesale` decimal(10,2) DEFAULT NULL,
  `Cost5-10` decimal(10,2) DEFAULT NULL,
  `Cost11-19` decimal(10,2) DEFAULT NULL,
  `Cost20` decimal(10,2) DEFAULT NULL,
  `Retail` decimal(10,2) DEFAULT NULL,
  PRIMARY KEY (`ItemID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$


delimiter $$

CREATE TABLE `tblItemCosts` (
  `Cost` decimal(10,2) DEFAULT NULL,
  `VendorID` int(11) NOT NULL,
  `ItemID` varchar(10) NOT NULL,
  KEY `VendorID_idx` (`VendorID`),
  KEY `ItemID_idx` (`ItemID`),
  CONSTRAINT `VendorID` FOREIGN KEY (`VendorID`) REFERENCES `tblVendors` (`VendorID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$


delimiter $$

CREATE TABLE `tblOrderItems` (
  `OrderItemID` int(11) NOT NULL AUTO_INCREMENT,
  `OrderNum` int(11) NOT NULL,
  `PayPalTxnID` int(10) DEFAULT NULL,
  `Description` varchar(225) DEFAULT NULL,
  `Quantity` int(11) DEFAULT NULL,
  `UnitPrice` decimal(10,2) DEFAULT NULL,
  `ItemStatus` varchar(30) DEFAULT NULL,
  `TrackingNumber` varchar(50) DEFAULT NULL,
  `ShippingCost` decimal(10,2) DEFAULT NULL,
  `ItemID` varchar(50) DEFAULT NULL,
  `TotalPrice` decimal(10,2) DEFAULT NULL,
  PRIMARY KEY (`OrderItemID`,`OrderNum`),
  UNIQUE KEY `PayPalTxnID_UNIQUE` (`PayPalTxnID`),
  KEY `PayPalTxnID_idx` (`PayPalTxnID`),
  KEY `UnitPrice_idx` (`ItemID`),
  KEY `OrderNum_idx` (`OrderNum`),
  CONSTRAINT `ItemID` FOREIGN KEY (`ItemID`) REFERENCES `tblCatalogItems` (`ItemID`),
  CONSTRAINT `OrderNum` FOREIGN KEY (`OrderNum`) REFERENCES `tblOrders` (`OrderNum`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `UnitPrice` FOREIGN KEY (`ItemID`) REFERENCES `tblCatalogItems` (`ItemID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=7678 DEFAULT CHARSET=latin1$$


delimiter $$

CREATE TABLE `tblOrderItemStatus` (
  `OrderItemID` int(11) NOT NULL,
  `OrderDate` varchar(12) DEFAULT NULL,
  `DesignProofSent` varchar(12) DEFAULT NULL,
  `SubmittedToProduction` varchar(12) DEFAULT NULL,
  `InProduction` varchar(12) DEFAULT NULL,
  `Shipped` varchar(12) DEFAULT NULL,
  PRIMARY KEY (`OrderItemID`),
  UNIQUE KEY `OrderItemID_UNIQUE` (`OrderItemID`),
  KEY `OrderItemID_idx` (`OrderItemID`),
  CONSTRAINT `OrderItemID` FOREIGN KEY (`OrderItemID`) REFERENCES `tblOrderItems` (`OrderItemID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$


delimiter $$

CREATE TABLE `tblOrders` (
  `OrderNum` int(11) NOT NULL AUTO_INCREMENT,
  `PayPalTxnID` int(10) DEFAULT NULL,
  `OrderDate` varchar(50) DEFAULT NULL,
  `OrderStatus` varchar(10) DEFAULT 'New',
  `RushFlag` bit(1) DEFAULT b'0',
  `ShipName` varchar(50) DEFAULT NULL,
  `ShipEmail` varchar(100) DEFAULT NULL,
  `ShipAddress1` varchar(50) DEFAULT NULL,
  `ShipAddress2` varchar(50) DEFAULT NULL,
  `ShipCity` varchar(50) DEFAULT NULL,
  `ShipState` char(2) DEFAULT NULL,
  `ShipZip` varchar(10) DEFAULT NULL,
  `ShippingCharge` decimal(10,2) DEFAULT NULL,
  `TotalCost` decimal(10,2) DEFAULT NULL,
  PRIMARY KEY (`OrderNum`),
  UNIQUE KEY `PayPalTxnID_UNIQUE` (`PayPalTxnID`)
) ENGINE=InnoDB AUTO_INCREMENT=346 DEFAULT CHARSET=latin1$$


delimiter $$

CREATE TABLE `tblVendors` (
  `VendorID` int(11) NOT NULL,
  `VendorName` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`VendorID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$

I tried the suggestion in this relevant post, but there were no results. This is a new database that hasn't actually been used yet; I've just filled it with fake data. Any ideas would be greatly appreciated.

Answer 1

There is a foreign key constraint on tblOrderItems that its ItemID needs to reference an ItemID that already exists in tblCatalogItems.

CONSTRAINT `ItemID` FOREIGN KEY (`ItemID`) REFERENCES `tblCatalogItems` (`ItemID`),

The message only means that you're trying to update tblOrderItems to reference the item in tblCatalogItems with ItemID= 0004, but that item does not exist.

Since ItemID is a varchar, you probably want to quote the 0004 or it may be converted to an int 4 before conversion to varchar. That may be your problem if the row with ItemID = 0004 actually exists.

UPDATE tblOrderItems SET `ItemID` = '0004' WHERE `OrderNum`= 203 AND `OrderItemID` = 26

Answer 2

Without seeing the table data I can't be sure, but I'm guessing it's because there is no record in tblCatalogItems with an ItemID of '0004'.

Also, you probably need to quote the 0004 in your update statement since the column is defined as character (varchar(10)) not number (int).

There is a foreign key relationship defined between tblCatalogItems.ItemId and tblOrderItems.ItemId which means that any row in tblOrderItems can only have a value for ItemId that matches an ItemId found in tblCatalogItems.

You would therefore need to insert a record into 'tblCatalogItems' with an ItemId of '0004' first, before running your update on tblOrderItems

Alternatively you need to change the SET ItemID = clause in your update to set a value that matches to an ItemId value that actually exists in the tblCatalogItems table

Answer 3

The data type needs to match on both sides of your foreign key constraint. Here you have a varchar(50) referring a varchar(10), which isn't allowed.

CREATE TABLE `tblCatalogItems` (
  `ItemID` varchar(10) NOT NULL DEFAULT '',
  ...
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$

...

CREATE TABLE `tblOrderItems` (
  `ItemID` varchar(50) DEFAULT NULL,
  ...
  CONSTRAINT `UnitPrice` FOREIGN KEY (`ItemID`) REFERENCES `tblCatalogItems` (`ItemID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=7678 DEFAULT CHARSET=latin1$$