MySQL 5.5 foreign key constraint fails when foreign key exists

Question

Just installed MySQL 5.5 on mac os x 10.6 and am having a strange issue on many tables. Below is an example. Inserting a row fails with a foreign key constraint when it sh

Answer 1

I had the same error today. In my case, I've used a script to recreate a few tables with all their records.

In fact, I've realised that "Engine" type was different between my tables: one was MyISAM and the second one (the reference of the FK) was InnoDB. I've altered all my tables to InnoDB and now everything works fine.

This script will generate an update script file (Reference)

mysql -u DB_USER -pDB_PASSWORD --default-character-set=utf8  DATABASE_NAME -e "SELECT CONCAT('ALTER TABLE ', table_name, ' ENGINE=InnoDB;') AS sql_statements FROM information_schema.tables AS tb WHERE table_schema = database() AND ENGINE = 'MyISAM' AND TABLE_TYPE = 'BASE TABLE' ORDER BY table_name DESC;" > ./alter_InnoDb.sql

You must remove the first line in "alter_InnoDb.sql", line containing the text "sql_statements".

After that, you can execute the script in your database to correct this error:

mysql -u DB_USER -pDB_PASSWORD --default-character-set=utf8  DATABASE_NAME < ./ alter_InnoDb.sql

Answer 2

Not surprising IMHO. I have found numerous bugs in MySQL. For example running queries with where clauses such as "WHERE some_tinyint_column = 0" would produce no data when it should, but rewriting the clause as "WHERE (NOT some_tinyint_column = 1)" produces results. After some research I found that it was a bug that was supposed to have been fixed, but in the release I was using, the bug was still there.

Conclusion: when something makes absolutely no sense in MySQL, I usually find it safe to assume it's a bug and start researching for info along those lines.

Answer 3

check the Numeric Type Attributes of Language_Phrases (Language_Id) and Language (Id)

both should be either UNSIGNED ZEROFILL or SIGNED

Answer 4

*mysql> INSERT INTO Language_Phrases (Language_Id, Label, Phrase) VALUES (1, 'exampleLabel', 'Some phrase'); ERROR 1452 (23000): Cannot add or update a child row:...*

You are trying to insert 1 as Language_Id, but table Language has property AUTO_INCREMENT=3. In this case you should use 3 or higher.

Answer 5

I was also facing the same issue and did not find any solution which solves my issue. So this issue can occur due to many reasons. I am just trying to put as many of these reasons and solutions at one place and also putting the fix which helped me to resolve this. I hope this will help someone in future.

1) Provided by Penfold - case sensitivity of table names
2) Engine mismatch in Parent and Child Table
3) Charset mismatch in Parent and Child Table
4) Parent(Id) and Child(Patent_Id : both must have exactly same data types (Also Signed/Unsigned)
5) InnoDB lost table but table exists - Please find solution here

SQL Query (show engine InnoDB status) gives this error (its .ibd file does not currently exist!) Blockquote

6) Few older versions of mysql has this bug.Bug#60196, Bug#60309
7) This works for me (if everything above seems fine, you probably needs this)- Dropping the foreign key from Child Table and Add Constraint again. If it also fails then drop parent table and create it again, before this you need to drop foreign key from all the Child Tables. This one is last possible thing.
Further Read :
https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_lower_case_table_names

Answer 6

This does appear to be a bug introduced since MySQL 5.5.9 on Mac OS X: http://bugs.mysql.com/bug.php?id=60309

It is marked as fixed in 5.5.13 (released May 31) and mentioned in the release notes: http://dev.mysql.com/doc/refman/5.5/en/news-5-5-13.html

Alternatively, there is a workaround listed in the bug report that I've verified on 5.5.10 and reproduced below:

[20 Mar 11:29] Harald Neiss

I also received a new MBP and reinstalled MySQL (mysql-5.5.10-osx10.6-x86_64). Finally I
came across the same problem as described above. So here is the query result and what I
did to solve it.

mysql> show variables like 'lower%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| lower_case_file_system | ON    |
| lower_case_table_names | 2     |
+------------------------+-------+
2 rows in set (0.00 sec)

Dropped database, created the file /etc/my.cnf with the following content:

[mysqld]
lower_case_table_names=1

Restarted the MySQL daemon and repeated the query:

mysql> show variables like 'lower%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| lower_case_file_system | ON    |
| lower_case_table_names | 1     |
+------------------------+-------+
2 rows in set (0.00 sec)

I recreated the tables and everything works fine.