MySQL supports foreign keys, which permit cross-referencing related data across tables, and foreign key constraints, which help keep the related data consistent. A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column values. A foreign key constraint is defined on the child table.ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
The error message “Cannot add or update a child row: a foreign key constraint fails” means that you are trying to add or update a row in a child table that does not have a matching row in the parent table. For example, if you have a table called customers and a table called orders, and you try to add an order for a customer that does not exist, you will get this error message.
There are a few ways to fix this error:
- Make sure that the row you are trying to add or update exists in the parent table.
- Disable the foreign key constraint on the child table. This will allow you to add or update the row, but it will also make it possible for you to have orphaned rows in the child table.
- Delete the row from the child table. This will remove the error, but it will also delete the data in the row.
The best way to fix this error depends on your specific situation. If you are sure that the row you are trying to add or update exists in the parent table, then you can just make sure that the foreign key constraint is enabled. If you are not sure if the row exists, then you can disable the foreign key constraint and then add or update the row. If you are sure that the row exists, but you do not want to delete it, then you can delete the row from the child table.
Here are some additional things to keep in mind:
- Foreign key constraints are used to enforce referential integrity in a database. Referential integrity means that the data in a database is consistent.
- Foreign key constraints can be enabled or disabled on a per-table basis.
- Disabling a foreign key constraint can make it possible to have orphaned rows in a child table. Orphaned rows are rows in a child table that do not have a matching row in the parent table.
- Deleting a row from a child table will also delete the data in the row.
Execute one of these lines before running your query, then you can run your query successfully. 🙂
1) For Session (recommended)
SET FOREIGN_KEY_CHECKS=0;
2) Globally
SET GLOBAL FOREIGN_KEY_CHECKS=0;
