Question

Usually I worked with PostgreSQL and never had a problem, but now I need to work with MySQL and I experiencing some troubles.
I am creating a table in database user_main_db. There is some problem with Foreign keys, phpMyAdmin always gives me next error:

1005 – Can’t create table ‘user_main_db.user_main’ (errno: 150) (

engine=InnoDB&page=Status&token=136fdbb820093986c79180b24adb304d”>Details…)

This is the table I am trying to create in database user_main_db:

CREATE TABLE user_main
(
uid INTEGER,
fn VARCHAR(40) NOT NULL,
ava VARCHAR(255),
gender tinyint(1) NOT NULL,
dob DATE NOT NULL,
country_id INTEGER, 
PRIMARY KEY (uid),
FOREIGN KEY ( uid ) REFERENCES user_basic_db.user_basic(uid) ON DELETE CASCADE ON UPDATE            CASCADE,
FOREIGN KEY ( country_id ) REFERENCES countries_db.countries(country_id) ON DELETE CASCADE   ON UPDATE CASCADE
);

This is table user_basic in database user_basic_db:

CREATE TABLE user_basic
(
uid INTEGER AUTO_INCREMENT,
email VARCHAR(40) NOT NULL,
password VARCHAR(40) NOT NULL,
PRIMARY KEY (uid)
);

This is table countries in database countries_db:

 CREATE TABLE countries(
    country_id INTEGER PRIMARY KEY AUTO_INCREMENT,
    country VARCHAR(40) NOT NULL UNIQUE
    )

The strange thing is when I define the table as follows:

CREATE TABLE user_main
(
uid INTEGER PRIMARY KEY REFERENCES user_basic_db.user_basic(uid)  ON DELETE CASCADE ON    UPDATE CASCADE,
 VARCHAR(40) NOT NULL,
ava VARCHAR(255),
gender tinyint(1) NOT NULL,
dob DATE NOT NULL,
country_id INTEGER REFERENCES countries_db.countries(country_id) ON DELETE CASCADE ON  UPDATE CASCADE
);

the query runs successfully but FOREIGN KEYS are not created, when I open ‘relational view’ there are no references to uid and country_id and I can make insert to user_main(country_id) even if there is no country with such id.
Please help someone. Thank you.

Answer 1

Check out the MySQL manual about foreign key constrains:

If you re-create a table that was dropped, it must have a definition
that conforms to the foreign key constraints referencing it. It must
have the right column names and types, and it must have indexes on the
referenced keys, as stated earlier. If these are not satisfied, MySQL
returns error number 1005 and refers to error 150 in the error
message.

Sounds familiar, doesn’t it!?

Better drop the tables and create it new with a well formed syntax, something like this:

CREATE TABLE `countries` (
  `country_id` int(11) NOT NULL AUTO_INCREMENT,
  `country` varchar(40) NOT NULL,
  PRIMARY KEY (`country_id`),
  UNIQUE KEY `country` (`country`)
) ENGINE=InnoDB;

CREATE TABLE `user_basic` (
  `uid` int(11) NOT NULL AUTO_INCREMENT,
  `email` varchar(40) NOT NULL,
  `password` varchar(40) NOT NULL,
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB;

CREATE TABLE `user_main` (
  `uid` int(11) NOT NULL,
  `fn` varchar(40) NOT NULL,
  `ava` varchar(255) DEFAULT NULL,
  `gender` tinyint(1) NOT NULL,
  `dob` date NOT NULL,
  `country_id` int(11) NOT NULL,
  PRIMARY KEY (`uid`),
  KEY `user_main_ibfk_2` (`country_id`),
  CONSTRAINT testc1
  FOREIGN KEY (`country_id`) REFERENCES `countries` (`country_id`) 
    ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT testc2
  FOREIGN KEY (`uid`) REFERENCES `user_basic` (`uid`) 
    ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB;

This should do the job.