3345
MariaDBERRORCommonDDL / Foreign KeysHIGH confidence
Cannot change child foreign key column
Production Risk
High — DDL fails; schema change is blocked until FK is handled.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE orders MODIFY customer_id BIGINT; -- if customer_id is a FK and parent column is INT
expected output
ERROR 3345 (HY000): Cannot change column 'customer_id' because it is used in a foreign key constraint.
Fix
Drop FK, alter, recreate
Drop FK, alter, recreate
ALTER TABLE orders DROP FOREIGN KEY fk_cust, MODIFY customer_id BIGINT, ADD CONSTRAINT fk_cust FOREIGN KEY (customer_id) REFERENCES customers(id);
Why this works
Dropping and recreating the FK lets you change both columns consistently.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 3345 ER_FOREIGN_KEY_COLUMN_CANNOT_CHANGE_CHILD
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