3407
MariaDBERRORNotableForeign KeysHIGH confidence
Foreign key child table has no index for the constraint
Production Risk
Low — DDL fails; no constraint is created.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE child ADD FOREIGN KEY (col) REFERENCES parent(id);
expected output
ERROR 3407 (HY000): Failed to add the foreign key constraint. Missing index for constraint.
Fix
Create index on child FK column
Create index on child FK column
ALTER TABLE child ADD INDEX idx_fk_col (col); ALTER TABLE child ADD FOREIGN KEY (col) REFERENCES parent(id);
Why this works
InnoDB can now use the index for efficient FK constraint checking.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 3407 ER_FK_NO_INDEX_CHILD
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