Error
Error Code:
1762
MariaDB Error 1762: Foreign Key Duplication
Description
This error occurs when an operation on a parent table, such as an INSERT or UPDATE, attempts to create or modify a record in a way that would violate a FOREIGN KEY constraint. Specifically, it means the resulting entry in the child table would duplicate an existing unique key, thus violating the child table's unique constraint.
Error Message
Foreign key constraint for table '%s', record '%s' would lead to a duplicate entry in a child table
Known Causes
3 known causesDuplicate Child Table Entry
An INSERT or UPDATE operation on the parent table attempts to create a new row in the child table where a unique key already exists for the foreign key value being referenced.
Schema Mismatch
The foreign key relationship or a unique constraint on the child table's referencing column is incorrectly defined, leading to unexpected duplication checks during parent table modifications.
Existing Data Inconsistencies
The child table already contains duplicate entries that violate its own unique constraints, making new foreign key operations problematic and triggering this error.
Solutions
3 solutions available1. Identify and Remove Duplicate Child Records medium
Find and delete duplicate entries in the child table that violate the foreign key constraint.
1
Identify the parent table and the specific record causing the foreign key duplication. The error message '%s', record '%s' usually provides this information.
TEXT2
Determine the child table and the columns involved in the foreign key relationship.
SHOW CREATE TABLE parent_table;
SHOW CREATE TABLE child_table;3
Query the child table to find duplicate entries based on the columns referenced by the foreign key. Replace `fk_column_in_child` with the actual column name in the child table and `parent_id_value` with the ID from the parent record causing the error.
SELECT fk_column_in_child, COUNT(*) FROM child_table WHERE fk_column_in_child = (SELECT id FROM parent_table WHERE ... /* condition for the problematic parent record */) GROUP BY fk_column_in_child HAVING COUNT(*) > 1;4
Carefully examine the identified duplicate records. Decide which records to keep and which to delete. It's often a good idea to back up the child table before proceeding.
SELECT * FROM child_table WHERE fk_column_in_child = <duplicate_parent_id>;5
Delete the excess duplicate records from the child table. Be extremely cautious with this step. Ensure you are deleting the correct records.
DELETE FROM child_table WHERE id IN ( /* subquery to select duplicate IDs to delete, keeping one */ );6
Retry the operation that initially caused the error.
TEXT2. Temporarily Disable and Re-enable Foreign Key Checks easy
A quick way to bypass the error for a single operation, useful for data migration or bulk inserts.
1
Begin a transaction to ensure atomicity.
START TRANSACTION;2
Temporarily disable foreign key checks.
SET FOREIGN_KEY_CHECKS = 0;3
Perform the operation that was causing the foreign key duplication error (e.g., INSERT, UPDATE).
/* Your problematic SQL statement here */4
Re-enable foreign key checks.
SET FOREIGN_KEY_CHECKS = 1;5
Commit the transaction.
COMMIT;3. Adjust Data Insertion Logic medium
Modify your application's data insertion logic to prevent duplicate child records from being created.
1
Review the application code responsible for inserting or updating records in the child table.
TEXT2
Before inserting a new record into the child table, query the child table to check if a record with the same foreign key value already exists.
SELECT COUNT(*) FROM child_table WHERE fk_column_in_child = ?;3
If the count is greater than 0, handle the situation appropriately. This might involve updating the existing record, skipping the insert, or raising an error to the user.
IF (record_exists) THEN
-- Handle existing record
ELSE
-- Insert new record
END IF;4
Consider using `INSERT IGNORE` if you want to silently ignore duplicate key errors on the foreign key column (assuming the child table has a unique constraint on the foreign key column or the combination that causes the duplication).
INSERT IGNORE INTO child_table (fk_column_in_child, other_columns) VALUES (?, ?);