I am trying to create a table Task that consists two columns which refer to the same table. The following code is generated by rails. When I tried the same code with SQLite everything worked fine. But I don't know why it does not work with Mysql... Hope you can help me!!! Thank you very much
CREATE TABLE `tasks` (`id` int AUTO_INCREMENT PRIMARY KEY,
`owner_id` int,
`assignee_id` int,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
INDEX `index_tasks_on_owner_id` (`owner_id`),
INDEX `index_tasks_on_assignee_id` (`assignee_id`),
CONSTRAINT `fk_rails_877a66d795`
FOREIGN KEY (`owner_id`)
REFERENCES `owners` (`id`),
CONSTRAINT `fk_rails_0016c50613`
FOREIGN KEY (`assignee_id`)
REFERENCES `assignees` (`id`)
) ENGINE=InnoDB
ERROR 1215 (HY000): Cannot add foreign key constraint
Related
I seem to have encountered an inconsistency in the way an ALTER TABLE statement behaves when dropping and adding a foreign key. Sometimes the associated index will be renamed and other times it isn't. I have identified the situations under which this occurs:
APPROACH #1
A simple person table with an auto-incrementing primary key id and a foreign key column to itself self_id. Note: the behaviour would be the same for two separate tables, I have used one table to simplify the example.
CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`self_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `self_id_fk` (`self_id`),
CONSTRAINT `self_id_fk` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Next I rename the foreign key by dropping the existing one and then adding a new one. This is done in a single statement but the behaviour is the same if split into multiple ALTER TABLE statements.
ALTER TABLE `person`
DROP FOREIGN KEY `self_id_fk`,
ADD CONSTRAINT `a_new_fk_name` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`);
After this statement the table is as follows:
CREATE TABLE `person` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`self_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `self_id_fk` (`self_id`),
CONSTRAINT `a_new_fk_name` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Notice that the foreign key has been renamed but the index has not.
APPROACH #2
An alternative way of doing this would be to first create the table without any foreign keys or indexes:
CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`self_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Next add the foreign key constraint:
ALTER TABLE `person` ADD CONSTRAINT `self_id_fk` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`);
This results in the following table:
CREATE TABLE `person` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`self_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `self_id_fk` (`self_id`),
CONSTRAINT `self_id_fk` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Note that an index is automatically created due to the behaviour described in the documentation
... an index is created on the referencing table automatically if it
does not exist
Next I rename the foreign key in the same way as APPROACH #1:
ALTER TABLE `person`
DROP FOREIGN KEY `self_id_fk`,
ADD CONSTRAINT `a_new_fk_name` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`);
But this time both the foreign key and the index have been renamed:
CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`self_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `a_new_fk_name` (`self_id`),
CONSTRAINT `a_new_fk_name` FOREIGN KEY (`self_id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Is there any explanation into what's going on? It's almost as if MySQL is tracking which indexes are "auto created" and then renaming them when the foreign key is changed. The Table DDL is identical for both approaches before the ALTER TABLE statement is run so there must be some "internal engine state" that MySQL is tracking.
Looking at the DDL alone there is no way to predict in which way MySQL will behave when the ALTER TABLE statement is run. This means that two "schema identical" databases could end up with mismatched schema once a simple ALTER TABLE statement has run.
I have noticed the same thing, but I've never seen any official documentation that explains this.
I agree it seems like InnoDB "knows" which indexes were created implicitly and which were created explicitly. But I don't know where it tracks this information. InnoDB exposes much of the metadata in INFORMATION_SCHEMA tables, but it must store more information in the internal data dictionary.
This is the only documentation about the internal DD in MySQL 5.7 and earlier: https://dev.mysql.com/doc/refman/5.7/en/innodb-data-dictionary.html
The only suggestion I have is that if you need the index name to be predictable, you need to create the index explicitly, then create the foreign key constraint. Don't rely on implicit creation of indexes by foreign keys.
MySQL 8.0 has totally redesigned the data dictionary, so the behavior you observe might change yet again. https://dev.mysql.com/doc/refman/8.0/en/data-dictionary.html
I have an odd one. I cannot create a table using the following:
The table Users already exists in the DB, only UserTimeZones is to be added, and it fails.
CREATE TABLE `Users` (
`AccessFailedCount` int(11) NOT NULL,
`EmailConfirmed` bit(1) NOT NULL,
`Id` char(36) NOT NULL,
`NormalizedUserName` varchar(256) DEFAULT NULL,
`NormalizedEmail` varchar(256) DEFAULT NULL,
PRIMARY KEY (`Id`),
UNIQUE KEY `UserNameIndex` (`NormalizedUserName`),
KEY `EmailIndex` (`NormalizedEmail`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `UserTimeZones` (
`Id` char(36) NOT NULL,
`UserId` char(36) NOT NULL,
`TimeZoneOffsetInSeconds` int NOT NULL,
`LastUpdatedAt` datetime(6) NOT NULL,
CONSTRAINT `PK_UserTimeZones` PRIMARY KEY (`Id`),
CONSTRAINT `FK_UserTimeZones_Users_UserId` FOREIGN KEY (`UserId`) REFERENCES `Users` (`Id`) ON DELETE CASCADE
);
SHOW ENGINE INNODB STATUS;
Here is what the status shows:
------------------------ LATEST FOREIGN KEY ERROR
2018-11-09 11:26:44 0x7f832c523700 Error in foreign key constraint of
table fifty/UserTimeZones:
FOREIGN KEY (UserId) REFERENCES Users (Id) ON DELETE CASCADE ):
Cannot find an index in the referenced table where the referenced
columns appear as the first columns, or column types in the table and
the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in tables
created with >= InnoDB-4.1.12, and such columns in old tables cannot
be referenced by such columns in new tables.
Please refer to
http://dev.mysql.com/doc/refman/5.7/en/innodb-foreign-key-constraints.html
for correct foreign key definition.
So I have the classic "Cannot add foreign key constraint".
What I have tried:
Placing the Users.Id column as first column : doesn't change anything
The column types are the same, the engines too...
Applying the migration without data in the DB -> it works
Running the script in a DB without data -> still doesn't work...
What is the problem?
Not sure it matters but I use entity framework core.
https://dev.mysql.com/doc/refman/8.0/en/innodb-foreign-key-constraints.html
Foreign key definitions for InnoDB tables are subject to the following
conditions:
InnoDB permits a foreign key to reference any index column or group of
columns. However, in the referenced table, there must be an index
where the referenced columns are listed as the first columns in the
same order.
But oddly the index seems to be needed on the referencing table:
https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html#foreign-keys-examples
So try adding an index on your table
CREATE TABLE `UserTimeZones` (
`Id` char(36) NOT NULL,
`UserId` char(36) NOT NULL,
`TimeZoneOffsetInSeconds` int NOT NULL,
`LastUpdatedAt` datetime(6) NOT NULL,
CONSTRAINT `PK_UserTimeZones` PRIMARY KEY (`Id`),
INDEX userid_ind (UserId),
CONSTRAINT `FK_UserTimeZones_Users_UserId` FOREIGN KEY (`UserId`) REFERENCES `Users` (`Id`) ON DELETE CASCADE
);
Note: this is what the error message says.
CREATE TABLE IF NOT EXISTS `demare`.`shop` (
`shop_id` INT NOT NULL AUTO_INCREMENT,
`shop_image` VARCHAR(255) NOT NULL,
`shop_price` FLOAT(6,2) NOT NULL,
`cart_id` INT NOT NULL,
PRIMARY KEY (`shop_id`),
INDEX `cart_id_idx` (`cart_id` ASC),
CONSTRAINT `cart_id`
FOREIGN KEY (`cart_id`)
REFERENCES `demare`.`shopping cart` (`cart_id`)
ON DELETE CASCADE
ON UPDATE NO ACTION)
ENGINE = InnoDB;
I have an error. My 'shop' table cannot be created as I have error:
121 Duplicate key on write or update.
I have provided the codes. Can anyone tell me what the problem is?
Problem exist because the foriegn key exist in memory, if possible drop the database and start again.
Hello my appologies for asking aid but i'm having a little issue in a database adding references
so i got a table
CREATE TABLE `kooien` (
`kooiid` INT(11) NOT NULL AUTO_INCREMENT,
`kooidlistppg` INT(11) NULL,
`quarantaine` BIT(1) NOT NULL,
`idvogelsoort` INT(11) NULL DEFAULT NULL,
`idvogelondersoort` INT(11) NULL DEFAULT NULL,
`vasteoflossekooie` BIT(1) NOT NULL,
`bezetofniet` BIT(1) NOT NULL,
`idlistsponsor` INT(11) NULL DEFAULT NULL,
PRIMARY KEY (`kooiid`),
INDEX `idvogelsoort` (`idvogelsoort`),
INDEX `idvogelondersoort` (`idvogelondersoort`),
INDEX `kooien_ibfk_4_idx` (`idlistsponsor`),
CONSTRAINT `kooien_ibfk_2` FOREIGN KEY (`idvogelsoort`) REFERENCES `vogelsoort` (`id`),
CONSTRAINT `kooien_ibfk_3` FOREIGN KEY (`idvogelondersoort`) REFERENCES `ondersoort` (`id`),
CONSTRAINT `kooien_ibfk_4` FOREIGN KEY (`idlistsponsor`) REFERENCES `personen` (`id`),
CONSTRAINT `FK_kooien_kooientoppg` FOREIGN KEY (`kooidlistppg`) REFERENCES `kooientoppg` (`id`))
COLLATE='utf8_general_ci'
ENGINE=InnoDB
Which appears like
kooiid|kooidlistppg|quarantaine|idvogelsoort|idvogelondersoort|Vasteoflossekooien|bezetofniet|lijstlist sponsor
Now my problem is making kooidlistppg references to kooidlistppg(id)
i do so with this query
ALTER TABLE `kooien`
DROP INDEX `FK_kooien_kooientoppg`,
ADD CONSTRAINT `FK_kooien_kooientoppg` FOREIGN KEY (`kooidlistppg`) REFERENCES `kooientoppg` (`id`);
/* SQL Fout (1215): Cannot add foreign key constraint */
ill add the create query for the table
CREATE TABLE `kooientoppg` (
`id` INT(11) NOT NULL,
`idpapegaaien` INT(11) NULL DEFAULT NULL
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
please know that its lack of a primary key is to convert a list to a mysql database
As explained in the MySQL manual, details of FOREIGN KEY errors with InnoDB can be checked with the following SQL command:
SHOW ENGINE INNODB STATUS
For example:
------------------------
LATEST FOREIGN KEY ERROR
------------------------
2017-01-22 23:43:46 0x7fc9fc0f1700 Error in foreign key constraint of table test/kooien:
FOREIGN KEY (`kooidlistppg`) REFERENCES `kooientoppg` (`id`))
COLLATE='utf8_general_ci'
ENGINE=InnoDB:
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-foreign-key-constraints.html for correct foreign key definition.
As far as I can tell, adding an index to the referenced column would help:
ALTER TABLE kooientoppg ADD INDEX id_idx (id);
I have two tables -
CREATE TABLE `FOO` (
`user_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
/*Nothing to see here*/
PRIMARY KEY (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=380 DEFAULT CHARSET=latin1;
CREATE TABLE `BAR` (
`ID` int(11) unsigned NOT NULL,
`UserID` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`ID`),
KEY `VSK_UserID_Index` (`UserID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
I am attempting create a foreign key constraint on BAR.UserID referencing users.user_id -
ALTER TABLE `FOO`.`BAR`
ADD CONSTRAINT `BAR_UserID_FKey`
FOREIGN KEY (`UserID`)
REFERENCES `FOO`.`users` (`user_id`)
ON DELETE CASCADE
ON UPDATE CASCADE;
I keep getting this error -
Operation failed: There was an error while applying the SQL script to the database.
Error 1452: Cannot add or update a child row: a foreign key constraint fails
Both of these tables have data in them - could this be the reason why this is happening, or is there something wrong with how the tables are being created?
Is there something I need to alter on one of these tables to make this work?
The data already in one of the tables (in particular, `FOO`.`BAR`, since that is the one you're adding a constraint to) is not consistent with the data in `FOO`.`users` (`user_id`).
You must ensure that the values un the `FOO`.`BAR`.`UserID` column all exist in `FOO`.`users` (`user_id`). There may be null values or other values that do not exist in the other column.