1553: Cannot drop index needed in a foreign key constraint

What does it mean?

You are trying to drop an index that is required by a foreign key constraint. InnoDB does not allow you to remove the index an FK relies on.

Why does it happen?

In InnoDB every foreign key requires an index on its referencing column(s). Dropping that index with DROP INDEX is rejected because it would leave the FK constraint without support. It usually comes up while reorganizing a table (index cleanup).

How to fix it

First drop the foreign key constraint, then drop the index: ALTER TABLE my_table DROP FOREIGN KEY fk_name; then DROP INDEX idx_name ON my_table; If needed, recreate the FK so that it relies on another suitable index. To list existing FKs: SELECT constraint_name, table_name FROM information_schema.key_column_usage WHERE referenced_table_name IS NOT NULL;