EC
1779
MySQLERRORNotableDDLHIGH confidence

ALTER TABLE operation not supported — specific reason

Production Risk

Medium — DDL blocked.

What this means

ALTER TABLE cannot use the specified algorithm/lock combination for this operation, and the error message includes the specific reason.

Why it happens
  1. 1The column or index change is incompatible with in-place or instant DDL.
  2. 2A foreign key change requires COPY algorithm.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE tbl ALGORITHM=INPLACE, ADD FOREIGN KEY (col) REFERENCES other(id); -- may require COPY

expected output

ERROR 1779 (0A000): ALTER TABLE ... ALGORITHM=INPLACE is not supported. Reason: ...

Fix

Switch to ALGORITHM=COPY or remove the ALGORITHM hint

Switch to ALGORITHM=COPY or remove the ALGORITHM hint
ALTER TABLE tbl ALGORITHM=COPY, ADD FOREIGN KEY (col) REFERENCES other(id);

Why this works

COPY algorithm supports all DDL operations.

What not to do

✕

Sources
Official documentation ↗

MySQL 8.0 — 1779 ER_ALTER_OPERATION_NOT_SUPPORTED_REASON

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