EC
3127
MySQLERRORNotableDDLHIGH confidence

ALTER TABLE not supported: table has no primary key

Production Risk

Medium — tables without PKs have poor InnoDB performance regardless of this error.

What this means

The requested in-place ALTER TABLE operation cannot proceed because the InnoDB table has no primary key, which is required for certain online DDL operations.

Why it happens
  1. 1InnoDB table was created without a PRIMARY KEY.
  2. 2Attempting an INPLACE operation that requires the clustered index.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE no_pk_table ADD COLUMN extra INT, ALGORITHM=INPLACE;

expected output

ERROR 3127 (HY000): ALGORITHM=INPLACE is not supported. Reason: Table has no primary key.

Fix

Add a primary key first

Add a primary key first
ALTER TABLE no_pk_table ADD COLUMN id INT AUTO_INCREMENT PRIMARY KEY FIRST, ALGORITHM=COPY;

Why this works

InnoDB works most efficiently with a primary key. Adding one enables more online DDL options.

What not to do

✕

Sources
Official documentation ↗

MySQL 8.0 — 3127 ER_ALTER_OPERATION_NOT_SUPPORTED_REASON_NOPK2

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