I'm trying to establish a many-to-many relationship within a table: a keyword can related to another keyword, and when that relation is added, the other direction must also be established.
Running on 10.5.9-MariaDB.
CREATE TABLE `related_keywords` (
`relation_id` int(12) NOT NULL AUTO_INCREMENT COMMENT 'Laravel/Eloquent pk crutch',
`keyword_1` bigint(20) unsigned NOT NULL,
`keyword_2` bigint(20) unsigned NOT NULL,
PRIMARY KEY (`relation_id`),
UNIQUE KEY `rel_kw_left_to_right` (`keyword_1`,`keyword_2`),
UNIQUE KEY `rel_kw_right_to_left` (`keyword_2`,`keyword_1`),
CONSTRAINT `fk_rel_kw_1_exists` FOREIGN KEY (`keyword_1`) REFERENCES `keywords` (`keyword_id`) ON DELETE CASCADE,
CONSTRAINT `fk_rel_kw_2_exists` FOREIGN KEY (`keyword_2`) REFERENCES `keywords` (`keyword_id`) ON DELETE CASCADE,
CONSTRAINT `fk_related_kw_lr` FOREIGN KEY (`keyword_1`, `keyword_2`) REFERENCES `related_keywords` (`keyword_2`, `keyword_1`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `ck_rel_kw_differ` CHECK (`keyword_1` <> `keyword_2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
In order to add one, the other must also be added. Likewise, removing one row must remove the other. However, I can't add the first one without adding the second one due to the foreign key check enforcing this:
INSERT INTO related_keywords (keyword_1, keyword_2) VALUES
(119250770368532480, 119251038153871360),
(119251038153871360, 119250770368532480);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`keyword_db`.`related_keywords`, CONSTRAINT `fk_related_keyword_lr` FOREIGN KEY (`keyword_1`, `keyword_2`) REFERENCES `related_keywords` (`keyword_2`, `keyword_1`) ON DELETE CASCADE ON UPDATE )
Now, I tried running it in a transaction, but it still seems to check the foreign keys (which I found odd). The only way that I can actually get it to add is to disable foreign key checks during the INSERT, which I really don't like.
The ideal solution here would be to make it so that, on the application level, all I had to do was:
INSERT INTO related_keywords (keyword_1, keyword_2) VALUES (119250770368532480, 119251038153871360);
and the matching row would be automatically added as well, with no problem from the fk_related_kw_lr foreign key check.
I've searched through docs for MariaDB and InnoDB in general and even with MariaDB 10.x's newer features I can't seem to work out a way to
Temporarily disable a single (out of several) constraint
Defer constraint checks until the end of the transaction
...and also insert the matching opposite-direction row when the first one is inserted
Any ideas?
The PK is useless
Only one UNIQUE is needed
3 uniques slows down inserts.
Optimal many-to-many: http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table
I doubt if you need "cascade".
Drop the FKs, they can be more trouble than they are worth.
Instead of adding 2 rows, consider adding one row with the following. (This may help or may complicate things, depending of what uses you have for this table.)
LEAST(1234, 2345),
GREATEST(1234, 2345)
I'm having a bit of a strange problem. I'm trying to add a foreign key to one table that references another, but it is failing for some reason. With my limited knowledge of MySQL, the only thing that could possibly be suspect is that there is a foreign key on a different table referencing the one I am trying to reference.
I've done a SHOW CREATE TABLE query on both tables, sourcecodes_tags is the table with the foreign key, sourcecodes is the referenced table.
CREATE TABLE `sourcecodes` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(11) unsigned NOT NULL,
`language_id` int(11) unsigned NOT NULL,
`category_id` int(11) unsigned NOT NULL,
`title` varchar(40) CHARACTER SET utf8 NOT NULL,
`description` text CHARACTER SET utf8 NOT NULL,
`views` int(11) unsigned NOT NULL,
`downloads` int(11) unsigned NOT NULL,
`time_posted` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `user_id` (`user_id`),
KEY `language_id` (`language_id`),
KEY `category_id` (`category_id`),
CONSTRAINT `sourcecodes_ibfk_3` FOREIGN KEY (`language_id`) REFERENCES `languages` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `sourcecodes_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `sourcecodes_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1
CREATE TABLE `sourcecodes_tags` (
`sourcecode_id` int(11) unsigned NOT NULL,
`tag_id` int(11) unsigned NOT NULL,
KEY `sourcecode_id` (`sourcecode_id`),
KEY `tag_id` (`tag_id`),
CONSTRAINT `sourcecodes_tags_ibfk_1` FOREIGN KEY (`tag_id`) REFERENCES `tags` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1
This is the code that generates the error:
ALTER TABLE sourcecodes_tags ADD FOREIGN KEY (sourcecode_id) REFERENCES sourcecodes (id) ON DELETE CASCADE ON UPDATE CASCADE
Quite likely your sourcecodes_tags table contains sourcecode_id values that no longer exists in your sourcecodes table. You have to get rid of those first.
Here's a query that can find those IDs:
SELECT DISTINCT sourcecode_id FROM
sourcecodes_tags tags LEFT JOIN sourcecodes sc ON tags.sourcecode_id=sc.id
WHERE sc.id IS NULL;
I had the same issue with my MySQL database but finally, I got a solution which worked for me.
Since in my table everything was fine from the mysql point of view(both tables should use InnoDB engine and the datatype of each column should be of the same type which takes part in foreign key constraint).
The only thing that I did was to disable the foreign key check and later on enabled it after performing the foreign key operation.
Steps that I took:
SET foreign_key_checks = 0;
alter table tblUsedDestination add constraint f_operatorId foreign key(iOperatorId) references tblOperators (iOperatorId); Query
OK, 8 rows affected (0.23 sec) Records: 8 Duplicates: 0 Warnings: 0
SET foreign_key_checks = 1;
Use NOT IN to find where constraints are constraining:
SELECT column FROM table WHERE column NOT IN
(SELECT intended_foreign_key FROM another_table)
so, more specifically:
SELECT sourcecode_id FROM sourcecodes_tags WHERE sourcecode_id NOT IN
(SELECT id FROM sourcecodes)
EDIT: IN and NOT IN operators are known to be much faster than the JOIN operators, as well as much easier to construct, and repeat.
Truncate the tables and then try adding the FK Constraint.
I know this solution is a bit awkward but it does work 100%. But I agree that this is not an ideal solution to deal with problem, but I hope it helps.
For me, this problem was a little different and super easy to check and solve.
You must ensure BOTH of your tables are InnoDB. If one of the tables, namely the reference table is a MyISAM, the constraint will fail.
SHOW TABLE STATUS WHERE Name = 't1';
ALTER TABLE t1 ENGINE=InnoDB;
This also happens when setting a foreign key to parent.id to child.column if the child.column has a value of 0 already and no parent.id value is 0
You would need to ensure that each child.column is NULL or has value that exists in parent.id
And now that I read the statement nos wrote, that's what he is validating.
I had the same problem today. I tested for four things, some of them already mentioned here:
Are there any values in your child column that don't exist in the parent column (besides NULL, if the child column is nullable)
Do child and parent columns have the same datatype?
Is there an index on the parent column you are referencing? MySQL seems to require this for performance reasons (http://dev.mysql.com/doc/refman/5.5/en/create-table-foreign-keys.html)
And this one solved it for me: Do both tables have identical collation?
I had one table in UTF-8 and the other in iso-something. That didn't work. After changing the iso-table to UTF-8 collation the constraints could be added without problems. In my case, phpMyAdmin didn't even show the child table in iso-encoding in the dropdown for creating the foreign key constraint.
It seems there is some invalid value for the column line 0 that is not a valid foreign key so MySQL cannot set a foreign key constraint for it.
You can follow these steps:
Drop the column which you have tried to set FK constraint for.
Add it again and set its default value as NULL.
Try to set a foreign key constraint for it again.
I'd the same problem, I checked rows of my tables and found there was some incompatibility with the value of fields that I wanted to define a foreign key. I corrected those value, tried again and the problem was solved.
I end up delete all the data in my table, and run alter again. It works. Not the brilliant one, but it save a lot time, especially your application is still in development stage without any customer data.
try this
SET foreign_key_checks = 0;
ALTER TABLE sourcecodes_tags ADD FOREIGN KEY (sourcecode_id) REFERENCES sourcecodes (id) ON DELETE CASCADE ON UPDATE CASCADE
SET foreign_key_checks = 1;
I had this exact same problem about three different times. In each instance it was because one (or more) of my records did not conform to the new foreign key. You may want to update your existing records to follow the syntax constraints of the foreign key before trying to add the key itself. The following example should generally isolate the problem records:
SELECT * FROM (tablename)
WHERE (candidate key) <> (proposed foreign key value)
AND (candidate key) <> (next proposed foreign key value)
repeat AND (candidate key) <> (next proposed foreign key value) within your query for each value in the foreign key.
If you have a ton of records this can be difficult, but if your table is reasonably small it shouldn't take too long. I'm not super amazing in SQL syntax, but this has always isolated the issue for me.
Empty both your tables' data and run the command. It will work.
I was getting this error when using Laravel and eloquent, trying to make a foreign key link would cause a 1452. The problem was lack of data in the linked table.
Please see here for an example: http://mstd.eu/index.php/2016/12/02/laravel-eloquent-integrity-constraint-violation-1452-foreign-key-constraint/
You just need to answer one question:
Is your table already storing data? (Especially the table included foreign key.)
If the answer is yes, then the only thing you need to do is to delete all the records, then you are free to add any foreign key to your table.
Delete instruction: From child(which include foreign key table) to parent table.
The reason you cannot add in foreign key after data entries is due to the table inconsistency, how are you going to deal with a new foreign key on the former data-filled the table?
If the answer is no, then follow other instructions.
I was readying this solutions and this example may help.
My database have two tables (email and credit_card) with primary keys for their IDs. Another table (client) refers to this tables IDs as foreign keys. I have a reason to have the email apart from the client data.
First I insert the row data for the referenced tables (email, credit_card) then you get the ID for each, those IDs are needed in the third table (client).
If you don't insert first the rows in the referenced tables, MySQL wont be able to make the correspondences when you insert a new row in the third table that reference the foreign keys.
If you first insert the referenced rows for the referenced tables, then the row that refers to foreign keys, no error occurs.
Hope this helps.
Make sure the value is in the other table otherwise you will get this error, in the assigned corresponding column.
So if it is assigned column is assigned to a row id of another table , make sure there is a row that is in the table otherwise this error will appear.
you can try this exapmple
START TRANSACTION;
SET foreign_key_checks = 0;
ALTER TABLE `job_definers` ADD CONSTRAINT `job_cities_foreign` FOREIGN KEY
(`job_cities`) REFERENCES `drop_down_lists`(`id`) ON DELETE CASCADE ON UPDATE CASCADE;
SET foreign_key_checks = 1;
COMMIT;
Note : if you are using phpmyadmin just uncheck Enable foreign key checks
as example
hope this soloution fix your problem :)
UPDATE sourcecodes_tags
SET sourcecode_id = NULL
WHERE sourcecode_id NOT IN (
SELECT id FROM sourcecodes);
should help to get rid of those IDs. Or if null is not allowed in sourcecode_id, then remove those rows or add those missing values to the sourcecodes table.
I had the same problem and found solution, placing NULL instead of NOT NULL on foreign key column. Here is a query:
ALTER TABLE `db`.`table1`
ADD COLUMN `col_table2_fk` INT UNSIGNED NULL,
ADD INDEX `col_table2_fk_idx` (`col_table2_fk` ASC),
ADD CONSTRAINT `col_table2_fk1`
FOREIGN KEY (`col_table2_fk`)
REFERENCES `db`.`table2` (`table2_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION;
MySQL has executed this query!
In my case, I created a new table with the same structure, created the relationships with the other tables, then extracted the data in CSV from the old table that has the problem, then imported the CSV to the new table and disabled foreign key checking and disabled import interruption, all my data are inserted to the new table that has no problem successfully, then deleted the old table.
It worked for me.
I want to delete a record from a school table without affecting a foreign key to the department name. I tried but I got this message:
"Cannot delete or update a parent row: a foreign key constraint fails
(arusms.department, CONSTRAINT department_ibfk_1 FOREIGN KEY
(school_name) REFERENCES school (school_name) ON UPDATE
CASCADE)"
I'm not sure why you would want to do that. If you delete the school, the department will be orphaned. That's the point of having foreign keys in the first place, to enforce referential integrity. If you want the department to remain and to be able to do this, you will need to alter the foreign key to include ON DELETE SET NULL. Otherwise, you will have to drop the constraint, perform the delete, and recreate the constraint.
Your error message is hiding the real cause.
(
arusms.department,
CONSTRAINT department_ibfk_1
FOREIGN KEY (school_name)
REFERENCES school (school_name)
ON UPDATE CASCADE
)
When you created the foreign key constarint, you omitted the ON DELETE part. MySQL used the default action for this, which is ON DELETE RESTRICT. See the MySQL docs: FOREIGN KEY Constraints
If you want to be able to delete schools without cascading effect to the related departments, you can either
remove the FK constraint or
make the column (department.school_name) nullable and alter the constraint to have the ON DELETE SET NULL action.
If you want to be able to delete schools and cascading deleting the related departments, you can
alter the constraint to have the ON DELETE CASCADE action.
The whole purpose of having a foreign key is to keep data consistent. In your case, it means that for each department, there must exist a corresponding school record. And if you DELETE a school, all corresponding departments should be deleted as well, or at least their school reference must be NULLed.
If you don't need this kind of enforcement, DROP the foreign key.
Alternatively, if you just want to reassign a department to another school, first do that, and only then DELETE the original school.
so I am working on a few tables and there are some data inconsistency between them... One or two tables have a foreign key constraint on a particular table (call it table X), but that table has multiple rows with the foreign key column.
What I want to do is to remove the duplicated rows in table X, but the foreign key constraint is preventing me from doing this. Is there a way to force delete the rows while ignoring the foreign key constraint since I know what I'm doing?
SET foreign_key_checks = 0;
That will prevent MySQL from checking foreign keys. Make sure to set it back to 1 when you are done though.
Also, you could always drop the foreign key and then add it later if you wanted to only affect a singular key
ALTER TABLE tableName DROP FOREIGN KEY fk;
Simply execute as follows:
Disable foreign key check
SET foreign_key_checks = 0;
Delete your records
DELETE FROM table_name WHERE {conditions};
Enable foreign key check
SET foreign_key_checks = 1;
Credit: https://www.knowledgewalls.com/johnpeter/books/mysql/how-to-ignore-constraints-while-insertupdate-or-delete-records-in-mysql
As some people already pointed out, ignoring a restricting foreign key leaves you with database inconsistencies. Preventing DELETEs is something you want in such cases.
You should better delete depending rows prior to the main query:
DELETE FROM cities WHERE country_id=3;
-- Afterwards you delete rows from the parent table without error:
DELETE FROM countries WHERE country_id=3;
Or, even better, change the foreign key once, so it does the deletion automatically (cascading):
ALTER TABLE cities DROP FOREIGN KEY `fk.cities.country_id`;
ALTER TABLE cities ADD CONSTRAINT `fk.cities.country_id` FOREIGN KEY (country_id)
REFERENCES countries (id) ON UPDATE CASCADE ON DELETE CASCADE;
-- From now on, just delete from the parent table:
DELETE FROM countries WHERE country_id=3;
To expand on the accepted answer, you have to specify the constraint name after DROP FOREIGN KEY
You can check the constraint name by issuing SHOW CREATE TABLE.
> SHOW CREATE TABLE tbl_name
Create Table: CREATE TABLE `tbl_name` (
`id` int(11) DEFAULT NULL,
`foo_id` int(11) DEFAULT NULL,
CONSTRAINT `foo_ibfk_1` FOREIGN KEY (`foo_id`)
)
In this case, "foo_ibfk_1" is the constraint name. So you can write:
ALTER TABLE tableName DROP FOREIGN KEY foo_ibfk_1;
In phpMyAdmin when i try to add foreign key some error occurs and does not tell what is wrong. Just says "FK fails".
Can any one tell what is the problem?
Error
SQL query:
ALTER TABLE `hotel` ADD FOREIGN KEY ( `type_id` ) REFERENCES `hotel`.`hotel_type` (
`id`
) ON DELETE CASCADE ON UPDATE CASCADE ;
MySQL said: Documentation
#1452 - Cannot add or update a child row: a foreign key constraint fails (`hotel`.`#sql-cfc_e`, CONSTRAINT `#sql-cfc_e_ibfk_2` FOREIGN KEY (`type_id`) REFERENCES `hotel_type` (`id`) ON DELETE CASCADE ON UPDATE CASCADE)
Be sure the columns of both tables are of the same data-type:
hotel.hotel type_id int(11) unsigned # type_id column of hotel table
hotel.hotel_type id int(11) unsigned # id column of hotel_type table
If they are not of the same type then you won't be able to add your FK constraint.
-- Edit --
Based on your response, the columns are the same data-types, so that means you have an invalid value in the hotels.type_id column (value doesn't exist in the hotel_types table). Check the values in your hotels.type_id column and make sure they exist in your hotel_types.id column.
Well there can be a lot of reasons for which you can't create a foreign key. I have found a very interesting article, which I suggest you to read it closely. Maybe something will help you. You can also find very important infos in the MySQL manual, regarding the "FOREIGN KEY Constraints".
Hope this helped.
There are some data in your table that no longer exist in other table, and actually this is against foreign key rules.
If you don't need their data, truncate both tables, and add the foreign key otherwise you should add all the foreign keys one by one.
Here is a query that will find those rows:
select sourcecode_id from
sourcecodes_tags tags left join sourcecodes sc on tags.sourcecode_id=sc.id
where sc.id is null;
Remove the ON DELETE CASCADE ON UPDATE CASCADE
Although this is old, I thought I would share that the way I resolved this was by checking that the encoding and the collation were the same on both sides which for some reason were different.
This fixed the issue.