MySQL foreign key creation with alter table command - mysql

Question

I created some tables using MySQL Workbench, and then did forward ‘forward engineer’ to create scripts to create these tables. BUT, the scripts lead me to a number of problems. One of which involves the foreign keys. So I tried creating separate foreign key additions using alter table and I am still getting problems. The code is below (the set statements, drop/create statements I left in … though I don’t think they should matter for this):
SET #OLD_UNIQUE_CHECKS=##UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET #OLD_FOREIGN_KEY_CHECKS=##FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET #OLD_SQL_MODE=##SQL_MODE, SQL_MODE='TRADITIONAL';
DROP SCHEMA IF EXISTS `mydb` ;
CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ;
-- -----------------------------------------------------
-- Table `mydb`.`User`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `mydb`.`User` ;
CREATE TABLE IF NOT EXISTS `mydb`.`User` (
`UserName` VARCHAR(35) NOT NULL ,
`Num_Accts` INT NOT NULL ,
`Password` VARCHAR(45) NULL ,
`Email` VARCHAR(45) NULL ,
`User_ID` INT NOT NULL AUTO_INCREMENT ,
PRIMARY KEY (`User_ID`) )
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`User_Space`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `mydb`.`User_Space` ;
CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` (
`User_UserName` VARCHAR(35) NOT NULL ,
`User_Space_ID` INT NOT NULL AUTO_INCREMENT ,
PRIMARY KEY (`User_Space_ID`),
FOREIGN KEY (`User_UserName`)
REFERENCES `mydb`.`User` (`UserName`)
ON UPDATE CASCADE ON DELETE CASCADE)
ENGINE = InnoDB;
SET SQL_MODE=#OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=#OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=#OLD_UNIQUE_CHECKS;
The error this produces is:
Error Code: 1005 Can't create table 'mydb.user_space' (errno: 150)
Anybody know what the heck I’m doing wrong?? And anybody else have problems with the script generation done by mysql workbench? It’s a nice tool, but annoying that it pumps out scripts that don’t work for me.
[As an fyi here’s the script it auto-generates:
SET #OLD_UNIQUE_CHECKS=##UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET #OLD_FOREIGN_KEY_CHECKS=##FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET #OLD_SQL_MODE=##SQL_MODE, SQL_MODE='TRADITIONAL';
DROP SCHEMA IF EXISTS `mydb` ;
CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ;
-- -----------------------------------------------------
-- Table `mydb`.`User`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `mydb`.`User` ;
CREATE TABLE IF NOT EXISTS `mydb`.`User` (
`UserName` VARCHAR(35) NOT NULL ,
`Num_Accts` INT NOT NULL ,
`Password` VARCHAR(45) NULL ,
`Email` VARCHAR(45) NULL ,
`User_ID` INT NOT NULL AUTO_INCREMENT ,
PRIMARY KEY (`User_ID`) )
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`User_Space`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `mydb`.`User_Space` ;
CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` (
`User_Space_ID` INT NOT NULL AUTO_INCREMENT ,
PRIMARY KEY (`User_Space_ID`) ,
INDEX `User_ID` () ,
CONSTRAINT `User_ID`
FOREIGN KEY ()
REFERENCES `mydb`.`User` ()
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
SET SQL_MODE=#OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=#OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=#OLD_UNIQUE_CHECKS;
**
Thanks!]

Answer 1

I haven't used MySQL Workbench to generate a lot of schemas, but I found the problem in the script. The foreign key definition in the User_Space table is attempting to create a foreign key on an unindexed column in the User table. If you alter the User definition to have an index on UserName, like this:
CREATE TABLE IF NOT EXISTS `mydb`.`User` (
`UserName` VARCHAR(35) NOT NULL ,
`Num_Accts` INT NOT NULL ,
`Password` VARCHAR(45) NULL ,
`Email` VARCHAR(45) NULL ,
`User_ID` INT NOT NULL AUTO_INCREMENT ,
PRIMARY KEY (`User_ID`),
INDEX(`UserName`)
)
ENGINE = InnoDB;
... the script will succeed. It sounds like MySQL Workbench probably isn't taking indexes into account when it generates the foreign key definitions. I'm not sure if you can fix this in your schema diagrams or if it's a bigger bug in the program, but I'd see if you could add index definitions in the right places and determine if that fixes the script generation.