I have two tables, books and borrowing requests - I am making a study project to learn MySQL. Trying to link these two tables using a FK, and constantly get an error:
"SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint")
Apart from documentation, I searched virtually all of the related topics here on SO, however, no success. Types are the same, columns both unsigned, one primary key, etc. - to my understanding I have respected all of the provisions. But it does not work! What am I missing?
Here are the two tables and the fk addition query:
CREATE TABLE `books` (
`book_id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`book_title` VARCHAR(100) NOT NULL,
`author_id` INT(11) NOT NULL,
`book_condition` INT(5) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=23453 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `borrowing_requests` (
`request_id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`user_id` INT(11) NOT NULL,
`book_id` INT(11) UNSIGNED NOT NULL,
`due_date` VARCHAR(55) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=23453 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
FK Query:
ALTER TABLE `books` ADD CONSTRAINT books_fk FOREIGN KEY (`book_id`)
REFERENCES `borrowing_requests`(`book_id`)
ON DELETE NO ACTION ON UPDATE NO ACTION
You have the foreign key "backwards" - the borrowing request should reference a book, not the other way round:
ALTER TABLE `borrowing_requests` ADD CONSTRAINT books_fk FOREIGN KEY (`book_id`)
REFERENCES `books`(`book_id`)
ON DELETE NO ACTION ON UPDATE NO ACTION
Related
Trying to create a simple relation between two fields in two tables - 'Task' table with the field 'USER_TOKEN' and the 'USER' table with the field 'TOKEN'. The two fields are the same structure. As you can see the error and other things that may assist you to help me understand the problem and fix it.
System: MacOS 10.12.3 | DB : MySQL 5.7.17 | DBM : Sequel Pro
Error : MySQL said: Cannot add foreign key constraint
CREATE TABLE `TASK` (
`ID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`USER_TOKEN` int(11) unsigned NOT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `USER` (
`ID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`TOKEN` int(11) unsigned NOT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE USER
ADD CONSTRAINT TOKENS
FOREIGN KEY (`TOKEN`) REFERENCES `category`(`USER_TOKEN`)
Thanks.
If you really want to create a foreign key to a non-primary key, it MUST be a column that has a unique constraint on it.
A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table.
So your USER_TOKEN column of table TASK and TOKEN column of USER table must be UNIQUE. So run the following query:
CREATE TABLE `TASK` (
`ID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`USER_TOKEN` int(11) unsigned NOT NULL UNIQUE,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `USER` (
`ID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`TOKEN` int(11) unsigned NOT NULL UNIQUE,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `USER`
ADD CONSTRAINT `TOKENS`
FOREIGN KEY (`TOKEN`) REFERENCES `TASK`(`USER_TOKEN`);
Check Demo here
I have a juction table that contains two foreign keys (from Profiles and Districts tables), with both columns as a composite primary key.
`profID` int(11) NOT NULL,
`distID` varchar(8) NOT NULL,
PRIMARY KEY (`profID`,`distID`)
I'd like to constrain both columns, but MySql throws an error:
#1050 - Table './database_name/z#002dprof#002ddist' already exists
In troubleshooting the problem, I've tried creating another duplicate junction table from scratch, but I get the same error. Oddly, MySQL will allow me to constrain one column or the other, but not both columns. I'm stumped, since I have other (non-junction) tables that have constraints on more than one foriegn key column.
By the way, I'm using phpMyAdmin, and all tables are InnoDB with utf-8.
Any help would be appreciated.
ADDED: SHOW CREATE TABLE results
CREATE TABLE `Profiles` (
`profID` int(11) NOT NULL AUTO_INCREMENT,
`email` varchar(64) NOT NULL,
`stID` varchar(2) NOT NULL,
`zip` varchar(5) NOT NULL,
PRIMARY KEY (`profID`),
KEY `stID` (`stID`,`zip`),
KEY `email` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=52 DEFAULT CHARSET=utf8
CREATE TABLE `Districts` (
`distID` varchar(8) NOT NULL,
`stID` varchar(2) NOT NULL,
`abbrev` varchar(16) NOT NULL,
PRIMARY KEY (`distID`),
KEY `stID` (`stID`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8
CREATE TABLE `z-prof-dist` (
`profID` int(11) NOT NULL,
`distID` varchar(8) NOT NULL,
PRIMARY KEY (`profID`,`distID`),
KEY `distID` (`distID`),
KEY `profID` (`profID`),
CONSTRAINT `z-prof-dist_ibfk_1` FOREIGN KEY (`distID`) REFERENCES `Districts` (`distID`)
ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8
I think I found a fix. Rather than using the phpMyAdmin function for adding a constraint (where I kept getting the error message), I instead followed marekful's lead by using an SQL ALTER TABLE query (with a new constraint name) as such:
ALTER TABLE `z-prof-dist`
ADD CONSTRAINT `test1`
FOREIGN KEY (`profID`) REFERENCES `Profiles` (`profID`)
ON UPDATE CASCADE
I still don't understand the cause of the original error, but I can see that the newly added foreign key constraint is working perfectly.
I've two InnoDB tables in a MySQL database. Now I like to link one table to the other with a FOREIGN KEY. But it aborts with the error code 1005 - Can't create table.
I've found plenty of information about this error. For example this post and answer here on SO. Although even this answer did not help in my case. I think every point which is mentioned to be checked is not true in my case.
I've created a MySQLFiddle you can checkout with the schema which fails: http://sqlfiddle.com/#!2/b9dc43
(Please note that the failing ALTER TABLE for adding the FOREIGN KEY is not included. See the schema below for the FOREIGN KEY query.)
There's also a FK for cms_element_instance.page_IDFK which references column page.ID but I removed this FK for posting my problem here on SO.
What can be the problem here?
Here the schema in plain text:
CREATE TABLE `cms_element_instance` (
`ID` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`page_IDFK` mediumint(8) unsigned DEFAULT NULL,
`revision` varchar(16) DEFAULT NULL,
PRIMARY KEY (`ID`),
KEY `page_IDFK` (`page_IDFK`)
) ENGINE=InnoDB AUTO_INCREMENT=1692 DEFAULT CHARSET=utf8;
CREATE TABLE `element_faq_list` (
`element_instance_IDFK` mediumint(8) unsigned NOT NULL,
`page_IDFK` mediumint(8) unsigned NOT NULL,
`mod_faq_collection_IDFK` mediumint(8) unsigned NOT NULL,
PRIMARY KEY (`element_instance_IDFK`,`page_IDFK`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- Create FK: This throws error 1005
ALTER TABLE element_faq_list
ADD CONSTRAINT element_instance_fk
FOREIGN KEY (element_instance_IDFK, page_IDFK)
REFERENCES cms_element_instance( ID , page_IDFK);
You are adding (element_instance_IDFK, page_IDFK) as a foreign key constraints which refers to ID , page_IDFK columns from cms_element_instance so for this case you need a primary key based on ID , page_IDFK columns
ALTER TABLE `cms_element_instance` CHANGE `page_IDFK` `page_IDFK`
MEDIUMINT(8) UNSIGNED NOT NULL, DROP PRIMARY KEY,
ADD PRIMARY KEY (`ID`, `page_IDFK`);
Demo
Many people had this problem already, but there was no fitting solution in other posts.
I have two tables, one named "sales", the other named "host_flags". I would like to have a foreign key for host_flags.sales_id to sales.id, but mysql won't let me! I have primary indexes defined in each table, so I wonder why...
The host_flags table already has a foreign key on the column host_id, but even when I tried and created the foreign key for the sales id first, it wouldn't let me.
The tables look like:
CREATE TABLE `sales` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`email` varchar(255) DEFAULT NULL,
`password` varchar(255) DEFAULT NULL,
`creation` datetime DEFAULT NULL,
`lastupdate` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;
CREATE TABLE `host_flags` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`host_id` int(11) DEFAULT NULL,
`sales_id` int(11) DEFAULT NULL,
`creation` datetime DEFAULT NULL,
`lastupdate` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `host_id6` (`host_id`),
CONSTRAINT `host_id6` FOREIGN KEY (`host_id`) REFERENCES `hosts` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `hosts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`creation` datetime NOT NULL,
`lastupdate` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=32225 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
I get this error message:
MySQL said: Can't create table 'primarydata.#sql-191_1' (errno: 150)
Thanks!
Charles
SOLUTION FOUND
All ints of the primary indexes have to be either signed or unsigned - not mixed.
Typically:
I like to declare the FK constraints outside of the table definition after all tables have been constructed.
ALTER TABLE `tbl`
ADD CONSTRAINT `constr`
FOREIGN KEY `fk_id` REFERENCES `ftbl`(`id`)
ON UPDATE CASCADE
ON DELETE CASCADE;
This way I can make sure the problem isn't something like the datatype of tbl.fk_id not being the same as the one of ftbl.id (including UNSIGNED as #Devart said). Or not having declared ftbl.id as unique. Regardless of the order of declaration of the tables.
After i do this i can integrate the constraint back into the table definition and take into account the order in which the tables need to be created to allow the constraint to be added.
You problem:
-- creating the sales table
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
-- creating the host_flags table
`sales_id` int(11) DEFAULT NULL,
-- the sales.id is declared as unsigned
-- the host_flags.sales_id is declared signed
Additonally to Recursed's answer:
There is a requirement that foreign keys contstraints' names must be unique in database scope. Maybe changing the name will work?
There is also a huge thread on MySQL community forums about the problem containing several solutions for some specific situations.
Possible two errors:
Reference and referenced columns must have the same type - int(11) unsigned
Unknown referenced table hosts.
I have two tables I have created and I'm adding the foreign key constraint after the fact.
The two tables are defined as such:
CREATE TABLE `user` (
`user_id` int(11) NOT NULL auto_increment,
`user_ad_id` varchar(500) default NULL,
`user_name` varchar(100) NOT NULL,
`login_id` varchar(100) default NULL,
`email` varchar(256) NOT NULL,
`personal_config` int(10) NOT NULL,
PRIMARY KEY (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
and
CREATE TABLE IF NOT EXISTS personal_config (
config_id INT(10) NOT NULL AUTO_INCREMENT,
last_updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
configuration TEXT(25600) NOT NULL,
PRIMARY KEY (config_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE personal_config ADD CONSTRAINT personal_config_fk_user FOREIGN KEY
(config_id) REFERENCES user(personal_config);
And I keep getting the same error but can't figure it out. I've searched all the related threads to this.
Your FK config_id can't be an autoincrement field, that doesn't make much sense right? That field reflects a value in the foreign table, it cannot be set arbitrarily in the local table.
I think this is what you want:
ALTER TABLE user ADD CONSTRAINT personal_config_fk_user FOREIGN KEY (personal_config) REFERENCES personal_config(config_id);
Your ALTER TABLE statement is backward. Since personal_config.config_id is an auto_increment primary key, the foreign key should be defined in the users table against personal_config, not in personal_config against the users table.
ALTER TABLE users ADD CONSTRAINT user_fk_personal_config
FOREIGN KEY (personal_config)
REFERENCES personal_config(config_id);
if you set your user table field personal_config is primary key then it is possible to execute
CREATE TABLE IF NOT EXISTS personal_config (
config_id INT(10) NOT NULL AUTO_INCREMENT,
last_updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
configuration TEXT(25600) NOT NULL,
PRIMARY KEY (config_id), FOREIGN KEY
(config_id) REFERENCES user(personal_config)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;