Using composite key as a foreign key in mysql - mysql

Question

My Tables
Fee Table
CREATE TABLE IF NOT EXISTS `fee` (
`feeNumber` int(11) NOT NULL,
`feeName` varchar(255) NOT NULL,
`feeDescription` varchar(255) DEFAULT NULL,
`feeAmount` varchar(255) NOT NULL,
`universityName` varchar(255) NOT NULL
)
ADD PRIMARY KEY (`feeNumber`,`feeName`,`feeAmount`)
Housing Table
CREATE TABLE IF NOT EXISTS `housing` (
`housingOfficeNumber` int(11) NOT NULL,
`housingOfficeName` varchar(50) NOT NULL DEFAULT '',
`housingOfficeType` varchar(50) DEFAULT NULL,
`housingOfficePhone` decimal(18,0) DEFAULT NULL,
`housingOfficeRoomDeposit` varchar(50) DEFAULT NULL,
`studentStatusName` varchar(50) DEFAULT NULL,
`housingFeeNumber` int(11) NOT NULL,
`housingFeeName` varchar(255) NOT NULL,
`housingFee` int(255) DEFAULT NULL,
`hOffTrm` varchar(50) DEFAULT NULL,
`universityName` varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
What I'm trying to do is reference the feeAmount,feeNumber, and feeName from the fee table and add it to the housingfee, housingfeeName, and housingFeenumber columns in the housing table. Since the feeAmount and feeName columns are not unique I decided to make a composite key out of feeNumber, feeName, and feeAmount. The only part of the composite key I really need referenced is feeAmount. feeName and feeNumber are not really important. using phpmyadmin.

Answer 1

No, no, no. In general, I think it is best to avoid compound primary keys. In this case, in particular, you do not want the fee amount or name to be part of the key. In order to access the row, you need to know the amount. That seems very difficult to implement.
I am guessing that an auto incremented primary key will work just fine. You can then add a separate unique constraint on other columns. So:
CREATE TABLE IF NOT EXISTS `fee` (
`feeNumber` int(11) NOT NULL auto_increment primary key,
`feeName` varchar(255) NOT NULL,
`feeDescription` varchar(255) DEFAULT NULL,
`feeAmount` varchar(255) NOT NULL,
`universityName` varchar(255) NOT NULL,
unique (feeName)
);
Then, another table would have feeNumber with an appropriate foreign key reference. Through the reference, you can get other information -- such as the name and amount -- using a join.