EC
1950
MySQLERRORCriticalConstraintHIGH confidence

Cannot delete or update a parent row: a foreign key constraint fails

Production Risk

High — referential integrity is being enforced correctly; fix the data or schema.

What this means

A DELETE or UPDATE on a parent table was blocked because a matching row exists in a child table with a FOREIGN KEY constraint that does not specify ON DELETE/UPDATE CASCADE or SET NULL.

Why it happens
  1. 1Deleting a parent row that is still referenced by one or more child rows.
  2. 2Updating the primary key of a parent row without cascading the change to child rows.
How to reproduce
trigger — this will error
trigger — this will error
DELETE FROM customers WHERE id = 1; -- child table orders still references id=1

expected output

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (mydb.orders, CONSTRAINT fk_cust FOREIGN KEY (customer_id) REFERENCES customers (id))

Fix 1

Delete or reassign child rows first

Delete or reassign child rows first
DELETE FROM orders WHERE customer_id = 1;
DELETE FROM customers WHERE id = 1;

Why this works

Remove dependent child records before deleting the parent.

Fix 2

Use ON DELETE CASCADE on the foreign key

Use ON DELETE CASCADE on the foreign key
ALTER TABLE orders DROP FOREIGN KEY fk_cust,
  ADD CONSTRAINT fk_cust FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE CASCADE;

Why this works

CASCADE automatically removes child rows when the parent is deleted.

What not to do

✕

Version notes

Sources
Official documentation ↗

MySQL 8.0 — 1950 ER_ROW_IS_REFERENCED_2

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