Mysql. Can't create table errno 150

I have to create a db with 2 tables in mysql but the script fails with errno 150 (Foreign key problem). I double-checked the foreign key fields to be the same on both tables and I can't find any error.

Here is the script:

 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 `testdb`;
 CREATE SCHEMA IF NOT EXISTS `testdb` DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci ;
 USE `testdb`;

 DROP TABLE IF EXISTS `testdb`.`table1` ;

 CREATE  TABLE IF NOT EXISTS `testdb`.`table1` (
   `id` INT UNSIGNED NOT NULL ,
   `field1` VARCHAR(50) NULL ,
   PRIMARY KEY (`id`) )
 ENGINE = InnoDB;



 DROP TABLE IF EXISTS `testdb`.`table2` ;

 CREATE  TABLE IF NOT EXISTS `testdb`.`table2` (
   `id` INT NOT NULL AUTO_INCREMENT ,
   `field1` VARCHAR(50) NULL ,
   `date` DATE NULL ,
   `cnt` INT NULL ,
   PRIMARY KEY (`id`) ,
   INDEX `FK_table2_table1` (`field1` ASC) ,
   CONSTRAINT `FK_table2_table1`
  FOREIGN KEY (`field1`)
  REFERENCES `testdb`.`table1` (`field1` )
  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;

I've tried it in Windows and Ubuntu with different versions of Mysql and didn't work.

 Answers

table1.field1 has no index defined on it.

It is required to place a FOREIGN KEY constraint on field1.

With this:

 CREATE  TABLE IF NOT EXISTS `testdb`.`table1` (
   `id` INT UNSIGNED NOT NULL ,
   `field1` VARCHAR(50) NULL ,
   KEY ix_table1_field1 (field1),
   PRIMARY KEY (`id`) )
 ENGINE = InnoDB;

Everything should then work as expected.

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Depending on the version of MySQL you may need to create an index on table1.field1 first.

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Another hint:

Even when your data types seem to be the same - in my case both columns had VARCHAR(50) - this is not enough.

You also need to make sure that both columns have the same COLLATION.

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Yet another cause, although slightly similar to others: I was referring to a table that turned out to have the MyISAM engine, instead of InnoDB.

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If nothing works, try this:

The foreign key name is a duplicate of an already existing key. Check that the name of your foreign key is unique within your database. Just add a few random characters to the end of your key name to test for this.

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In my case, one table was using foreign key constraints on another table that didn't exist yet. This was happening due to a large makefile, so it wasn't as obvious as I would've expected.

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I was using MySQL workBench. THe issue is you cannot use the same foreign key name, they need to be unique. So if more than one table will reference the same foreign key, each time there must be a unique name given.

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In my case I got old table definition MyISAM in one of the tables and obviously I was unable to make foreign key to it from another table. Maybe this help someone.

So this may happen because of inconsistencies between two databases/fields definitions try to check:

Field Type
Field Collation
Table Engine

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You also may encounter the same error when attempting to reference a composite key in your foreign key.

For example:

CREATE TABLE `article` (
  `id` int(10) unsigned NOT NULL,
  `type` enum('X','Y','Z') NOT NULL,
  PRIMARY KEY (`id`,`type`)
) ENGINE InnoDB;

CREATE TABLE `t1` (
  `user_id` int(10) unsigned NOT NULL,
  `type` enum('X','Y','Z') NOT NULL,
  `article_id` int(10) unsigned NOT NULL,
  CONSTRAINT `user_access_article_ibfk_2` FOREIGN KEY (`article_id`, `type`) REFERENCES `article` (`id`, `type`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB

In this case, it is important to use article_id and type field in the FK definition in the very same order as they appear in the article table PRIMARY KEY definition.

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In very strange cases your database might be broken. In my case I did not have any foreign keys on the table and the only renaming the table or changing engine helped.

Turned out innoDB was broken, see: https://dba.stackexchange.com/questions/86853/1025-error-on-rename-of-table-errno-150-table-was-deleted-while-tried-to-a?lq=1

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I got this error while trying to use a foreign key to reference a non-unique field. (which apparently is not allowed)