我正在创建两个表，在其中一个表中，我试图分配一个外键，但它给了我一个错误

Question

I am creating two tables one Platforms table and one game table and I am getting an error saying that it can not find PLATFORMID in sql statment but I don't understand why

Column "PLATFORMID" not found; SQL statement: CREATE TABLE game( gameId LONG PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), publisher VARCHAR(255), platform VARCHAR(255), price DECIMAL(4,2), FOREIGN KEY (platformId) REFERENCES Platforms(platformId) ) [42122-200]

This is my code for creating my tables

 CREATE TABLE Platforms(
     platformId LONG PRIMARY KEY AUTO_INCREMENT,
     platformName VARCHAR(255)
);

CREATE TABLE game(
    gameId LONG PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), publisher VARCHAR(255), platform VARCHAR(255), price DECIMAL(4,2),
         FOREIGN KEY (platformId) REFERENCES Platforms(platformId)
); 

Answer 1

The error is because a platformId reference is not found in the game table.

A few things to note:

1. The LONG data type is an alias for MEDIUMTEXT , which surely would not have AUTO_INCREMENT ? I get an error with the use as-is.
2. When you do FOREIGN KEY (platformId) , this portion refers to a column in the current table , and then the other table that this column refers to is the: REFERENCES Platforms(platformId) portion.
3. The foreign key's (column) reference in the current table must have an index.
4. It's critical to know that the column reference in BOTH tables for the foreign key must have the same data type , including signed-ness, if specified. (For example, if one column has unsigned, then other column needs to be unsigned too)

So, knowing those things, in the example below:

1. I've replaced LONG with INT(11) unsigned in both tables.
2. Added a column for platformId in the game table
3. Adds an index to the platformId column in the game table as well.

Putting all that together, here's an example interaction:

root@localhost((none)) use test2;
Database changed

root@localhost(test2) show tables;
Empty set (0.00 sec)

root@localhost(test2) CREATE TABLE Platforms(
    ->      platformId INT(11) unsigned PRIMARY KEY AUTO_INCREMENT,
    ->      platformName VARCHAR(255)
    -> );
Query OK, 0 rows affected (0.21 sec)

root@localhost(test2) CREATE TABLE game(
    ->     gameId INT(11) unsigned PRIMARY KEY AUTO_INCREMENT,
    ->     name VARCHAR(255),
    ->     publisher VARCHAR(255),
    ->     platform VARCHAR(255),
    ->     platformId INT(11) unsigned,
    ->     price DECIMAL(4,2),
    ->     index(platformid),
    ->     FOREIGN KEY (platformId) REFERENCES Platforms(platformId)
    -> );
Query OK, 0 rows affected (0.24 sec)

root@localhost(test2) show tables;
+-----------------+
| Tables_in_test2 |
+-----------------+
| game            |
| platforms       |
+-----------------+
2 rows in set (0.00 sec)

root@localhost(test2) show create table game \G
*************************** 1. row ***************************
       Table: game
Create Table: CREATE TABLE `game` (
  `gameId` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `publisher` varchar(255) DEFAULT NULL,
  `platform` varchar(255) DEFAULT NULL,
  `platformId` int(11) unsigned DEFAULT NULL,
  `price` decimal(4,2) DEFAULT NULL,
  PRIMARY KEY (`gameId`),
  KEY `platformId` (`platformId`),
  CONSTRAINT `game_ibfk_1` FOREIGN KEY (`platformId`) REFERENCES `platforms` (`platformId`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)