I have a clients, feedback and a repairs tables. A client can give many feedbacks and have many repairs. In the feedback table I have created a clientid column (added also index) and I am able to create a foreign key to the clientid column (primary key) of the clients table.
The problem is that I am unable to do the same with the repairs table. Even though I have created a clientid column (indexed) within the repairs table and it has the same properties as the clientid within the clients table I get the following:
MySQL said: Documentation
#1452 - Cannot add or update a child row: a foreign key constraint
fails (ccsdb.,
CONSTRAINT #sql-3f0_8e5_ibfk_1 FOREIGN KEY (client_id) REFERENCES
clients (client_id) ON DELETE CASCADE ON UPDATE CASCADE)
That error (Cannot add or update a child row: a foreign key constraint fails) is referenced in the MySQL FK Doc
To add a reference between 2 tables the condition must fit for existing data.
That means if you say table1.id = table2.id then all ids of table1 and table2 must match together.
To solve that you have to eliminate or fix those rows that don't match.
Example:
table1.id | table2.fk
1 | 1 ok
2 | null error
3 | 4 error if id 4 is not in table1
Related
First table users
id name
---------------------
1 John
Second table orders
id order name
----------------------------------
1 pencil John
The sql code to make a relationship with first column name in table users
And second column name in table orders
ALTER TABLE orders
ADD CONSTRAINT user_name
FOREIGN KEY(name) REFERENCES users(name)
ON UPDATE CASCADE
ON DELETE CASCADE;
it give me error
errno: 150 "Foreign key constraint is incorrectly formed"
How to Fix this proplem ??
So after searching I found that the solution is very simple :D
use the same sql code
ALTER TABLE orders
ADD CONSTRAINT user_name
FOREIGN KEY(name) REFERENCES users(name)
ON UPDATE CASCADE
ON DELETE CASCADE;
and make name unique in the parent column .
I'm designing a website of book library for my project in php.
Anyways I have three tables named books,users and savebook.
Table book has following columns: "bookid", "title","author" "genre" and "summary".
And table users has following columns userid, username, password, and name.
Users can save books as favorites and those saved books are saved in the table named savebook with columns bookid and userid which are foreign key to table book and users
I used following query for that:
ALTER TABLE savebook
ADD CONSTRAINT bkid_usid
FOREIGN KEY (bookid)
REFERENCES books (bookid);
and
ALTER TABLE savebook
ADD CONSTRAINT usid_bkid
FOREIGN KEY (userid)
REFERENCES users(userid);
Now the problem is whenever i try to delete a book from table book using query
DELETE FROM books
WHERE bookid=1;
I get this message:
1451 - Cannot delete or update a parent row: a foreign key constraint fails (booklibrary.savebook, CONSTRAINT bkid_usid FOREIGN KEY (bookid) REFERENCES books (bookid))
How do i delete a book from table book which also deletes the related row in table savebook?
To get the behavior you describe, you can specify
ON DELETE CASCADE
as part of the foreign key definition.
Reference: http://dev.mysql.com/doc/refman/5.5/en/create-table-foreign-keys.html
If you were to modify your foreign key constraint bkid_usid (on the booksave table), then the delete statement that you show
DELETE FROM books WHERE ...
Would cause MySQL to delete the rows in booksave that have a foreign key values that reference rows being removed from books.
ALTER TABLE savebook
ADD CONSTRAINT bkid_usid
FOREIGN KEY (bookid)
REFERENCES books (bookid)
ON DELETE CASCADE
;
Make note of that last line I added to the ALTER from the original question, it is an optional part of the foreign key definition (there is also ON UPDATE ...). By default, when not specified, I believe MySQL treats it as NO ACTION or RESTRICT (those two are effectively the same as far as I know) instead of CASCADE. Full documentation found at http://dev.mysql.com/doc/refman/5.6/en/create-table-foreign-keys.html
An interesting question :)
I think the problem is caused by the so called "referential integrity".
That means, that you are not able to delete a dataset, which primary key is used in another tables dataset as foreign key. If you could do this, some foreign keys of the table savebook would refer to a dataset in table books, that doesn't exist anymore.
So first you have to delete all datasets in savebook, where the bookid is the same one as of the book you want to delete and after that, you can delete this dataset from books. ;)
You have applied constraints to the tables. You need to tell MySQL to delete referenced entries from "savebook" table if any entry is deleted from "book" table.
ALTER TABLE savebook ADD CONSTRAINT bkid_usid FOREIGN KEY (bookid) REFERENCES books (bookid) ON DELETE CASCADE
I would like to know how can I relate 2 id's. One frome users table and another from stats table. The id from users is AI , Primary and I want to relate the other id to this one.
I tried Foreign key constraint (INNODB) and it gave me this error #1452 - Cannot add or update a child row: a foreign key constraint fails (game.#sql-3de_34f, CONSTRAINT ?sql?3de_34f_ibfk_1 FOREIGN KEY (id) REFERENCES user (id)) .
Thanks
Try this!
SET foreign_key_checks = 0;
Then run query to add your key, and after that...
SET foreign_key_checks = 1;
You have USER_IDs in your "stats" table that are not in your "users" table.
Delete them if you think they are not useful anymore.
DELETE FROM stats where user_id NOT IN (SELECT user_id from users);
Then, you can create your reference keys.
I am relatively new in php and mysql.The problem that i am facing while i inserting value in my leave table.My leave table containing following column..
1.lid(INT primary key)
2.empname(varchar)
3.username(varchar)
4.nod(INT)
5.sdate(DATE)
6.edate(DATE)
7.reason(varchar)
8.action(varchar)
9.empID (INT FOREIGN KEY)
here empID is the foreign key references from users table. The problem that im facing while inserting values into the leave table.ERROR is given below
Cannot add or update a child row: a foreign key constraint fails (db_attendance1.leave, CONSTRAINT leave_ibfk_1 FOREIGN KEY (empID) REFERENCES users (empID))
here i just send the query and here it is..
mysql_query("INSERT INTO `leave`
(`empname`, `username`,
`nod`, `sdate`, `edate`,
`reason`,`action`)
VALUES ('$empname', '$username',
'$nod', '$sdate',
'$edate', '$reason','');",
$dbCon) or die(mysql_error());
You can put
SET FOREIGN_KEY_CHECKS=0;
and run your query. Once you are done again set it back to 1 by
SET FOREIGN_KEY_CHECKS=1;
A foreign key constraint means that you one table doesn't accept inserts, updates or deletes that would 'break' the foreign key. This means, you can't update a EmpID if the new EmpID doesn't exist in the users. You can't add a new EmpID if it doesn't exist in the users table, etcetera.
So to solve this issue, you need to make sure that the EmpID you're trying to add to table 'leave', first exists in table 'users'.
Foreign keys can be a real powerful item, but can be a real pain too. Since the DB you're working on had foreign key constraints, I suggest you read on them a bit: http://en.wikipedia.org/wiki/Foreign_key
Borniet, you helped me solve my similar problem.
#OP - All I had to do to fix this was create a corresponding row in the table so that the foreign key would exist.
E.g. Table 1 has column Name
Table 2 has column friends_name, a foreign key tied to Name in table 1.
I got this error because I was trying to insert a row into table 2, where the friends_name referenced a non existing Name in table 1. So I created the name and we're off to the races :).
So the scenario is this:
I create a group with a form, stored in test_groups_tb, then with another form enter user ids to attach them to the group and they are stored in group_association_tb with a structure like so:
group_id | user_id
I am very new to MySQL and more so Foreign Key relationships, so I tried to set up a relationship on group_association_tb which was basically, if the group was deleted, delete all records of that group from group_association_tb.
now what Is happening since applying this is the group is stored fine. I can add students manually fine, but when I try adding them by importing a csv it doesn't like it.
here is the queries (i know its not efficient querying every iteration):
while($row = mysql_fetch_assoc($result))
{
$sql = "INSERT INTO group_association_tb (group_id, user_id)VALUES('$group','".$row[user_id]."')";
mysql_query($sql) or die(header("Location:error.php"));
}
here is the error i get:
Cannot add or update a child row: a foreign key constraint fails (`ece70141/group_association_tb`, CONSTRAINT `group_association_tb_ibfk_1` FOREIGN KEY (`group_id`) REFERENCES `test_groups_tb` (`group_id`) ON DELETE CASCADE)
could somebody explain what the problem is here.
many thanks,
For those encountering the problem " ERROR 1216: Cannot add or update a child row: a foreign key constraint fails", it actually means what it says! Some row in the child does not comply with the constraint, correct the problem.
You find the rows like this:
select child.id from child left join parent on (child.parent_id=parent.id) where child.id is not null and parent.id is null;
(from http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html)
EDIT: I think that you need to invert the constraint. test_groups_tb needs to reference the grop_association_tbl.
It looks like you have not added the group_id that you are referencing from the group_association_tb table to the test_group_tb table. If a foreign key from group_association_tb references a key in test_group_tb, the key has to be in test_group_tb before you can add it to group_association_tb.
For instance:
I have a table (user_group)_ defined as follows:
group_id, first_name, last_name
And another (group_permission) as follows:
group_id, permission_name
if I create a foreign key from group_permission that references user_group, I cannot add a row to group_permission with a group_id that doesn't exist in user_group already. First, I have to create the row in user_group with a given group_id, then insert into the group_permission table with the group_id of the associated row in user_group.