How to fix 'MySQL Error: 1822. Missing index for contraint' On creating a composite foreign key - mysql

Question

I'm trying to create a table with a composite foreign key, but keep getting met with the error Error Code: 1822. Failed to add the foreign key constraint. Missing index for constraint 'fk_contractdateshistoric_contractdates_multiple' in the referenced table 'contractdates'
I'm using MySQL v8.0.16
I've checked if the column types are different, and I'm not sure what else could be the problem.
Here are the tables that make up the problem, All tables are made happily but the last one that contains the composite key causes the problem.
CREATE TABLE `contracts` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`Name` varchar(100) DEFAULT NULL,
`CreationDate` datetime DEFAULT NULL,
`CreatedBy` varchar(30) DEFAULT NULL,
`CompletionDate` date DEFAULT NULL,
`Comments` varchar(100) DEFAULT NULL,
PRIMARY KEY (`ID`)
);
CREATE TABLE `fieldheading` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`fieldTypeID` int(11) DEFAULT NULL,
`fieldCode` int(11) DEFAULT NULL,
`fieldHeading` varchar(100) DEFAULT NULL,
PRIMARY KEY (`ID`)
);
CREATE TABLE `contractdates` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`DateValue` datetime DEFAULT NULL,
`ContractID` int(11) NOT NULL,
`FieldHeadingID` int(11) NOT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `uq_contractdates_contractID_FieldHeading_ID` (`ContractID`,`FieldHeadingID`),
KEY `fk_contractdates_contracts_id_idx` (`ContractID`),
KEY `fk_contractdates_fieldheading_id_idx` (`FieldHeadingID`),
CONSTRAINT `fk_contractdates_fieldheading_id` FOREIGN KEY (`FieldHeadingID`) REFERENCES `fieldheading` (`id`),
CONSTRAINT `fk_contractdates_contracts_id` FOREIGN KEY (`ContractID`) REFERENCES `contracts` (`id`)
) COMMENT='Table to hold the dates for a contract, one row is one date for a specific contract';
CREATE TABLE `contractdateshistoric` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`ContractID` int(11) NOT NULL,
`ContractDateCurrentID` int(11) NOT NULL,
`FieldHeadingID` int(11) NOT NULL,
`ChangedByID` int(11) NOT NULL,
`DateValue` datetime NOT NULL,
`TimeStampChanged` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`ID`),
KEY `fk_contractdateshistoric_contractdates_mutiple_idx` (`ContractID`, `FieldHeadingID`, `ContractDateCurrentID`),
CONSTRAINT `fk_contractdateshistoric_contractdates_multiple` FOREIGN KEY (`ContractID`, `FieldHeadingID`, `ContractDateCurrentID`) REFERENCES `contractdates` (`contractid`, `fieldheadingid`, `id`)
) COMMENT='Audit trail of the dates';

Answer 1

Since you are using Composite FK in the table contractdates try adding composite index as well
KEY `fk_contractdates_mutiple_idx` (`ContractID`,`FieldHeadingID`,`ID`)
Whole create statement
CREATE TABLE `contractdates` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`DateValue` datetime DEFAULT NULL,
`ContractID` int(11) NOT NULL,
`FieldHeadingID` int(11) NOT NULL,
PRIMARY KEY (`ID`),
KEY `fk_contractdates_contracts_id_idx` (`ContractID`),
KEY `fk_contractdates_fieldheading_id_idx` (`FieldHeadingID`),
KEY `fk_contractdates_mutiple_idx` (`ContractID`,`FieldHeadingID`,`ID`),
CONSTRAINT `fk_contractdates_fieldheading_id` FOREIGN KEY (`FieldHeadingID`) REFERENCES `fieldheading` (`id`),
CONSTRAINT `fk_contractdates_contracts_id` FOREIGN KEY (`ContractID`) REFERENCES `contracts` (`id`)
) COMMENT='Table to hold the dates for a contract, one row is one date for a specific contract';

Answer 2

It's trying to tell you "you haven't created a necessary unique index on contractdates, that covers the columns (contractid, fieldheadingid, id) so I cannot create a foreign key on contractdateshistoric that refers to this set of columns when determining the single parent row"
I'm not sure why you're creating an fk that references 3 columns when contractdates has a pk that is just the ID column.
If a contractdateshistoric records refers to a single contractdates record as its parent, the historic record should have a contractdateid column that refers to contractdates.id - no need for multiple columns. Copy the pattern you used to relate a contractdates to its parent contract, and you'll be fine

Answer 3

I have tried by creating the keys individually for the columns, Please find the updated query:
CREATE TABLE `contractdateshistoric` (
`ID` INT(11) NOT NULL AUTO_INCREMENT,
`ContractID` INT(11) NOT NULL,
`ContractDateCurrentID` INT(11) NOT NULL,
`FieldHeadingID` INT(11) NOT NULL,
`ChangedByID` INT(11) NOT NULL,
`DateValue` DATETIME NOT NULL,
`TimeStampChanged` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`ID`),
KEY `fk_contractdateshistoric_contractdates_mutiple_idx` (`ContractID`),
KEY `fk_contractdateshistoric_contractdates_mutiple_idx1` (`FieldHeadingID`),
KEY `fk_contractdateshistoric_contractdates_mutiple_idx2` (`ContractDateCurrentID`),
CONSTRAINT `fk_contractdateshistoric_contractdates_multiple` FOREIGN KEY (`ContractID`)
REFERENCES `contractdates` (`contractid`),
CONSTRAINT `fk_contractdateshistoric_contractdates_multiple1` FOREIGN KEY (`FieldHeadingID`)
REFERENCES `contractdates` (`fieldheadingid`),
CONSTRAINT `fk_contractdateshistoric_contractdates_multiple2` FOREIGN KEY (`ContractDateCurrentID`)
REFERENCES `contractdates` (`id`)
);
It works fine.