EC
1221
MySQLERRORNotableLockingHIGH confidence

Cannot combine WRITE locks for system and user tables

Production Risk

Low — operation fails safely; restructure locking strategy.

What this means

ER_WRONG_LOCK_OF_SYSTEM_TABLE (1221, SQLSTATE HY000) is raised when a LOCK TABLES statement tries to acquire WRITE locks on both system tables (e.g., mysql.user) and regular user tables simultaneously.

Why it happens
  1. 1Including both mysql.* system tables and user-defined tables in a single LOCK TABLES ... WRITE statement
How to reproduce
trigger — this will error
trigger — this will error
LOCK TABLES mysql.user WRITE, my_app.orders WRITE;  -- ERROR 1221

expected output

ERROR 1221 (HY000): You can't combine write-locking of system and user tables

Fix

Lock system tables and user tables separately

Lock system tables and user tables separately
-- Lock only user tables
LOCK TABLES my_app.orders WRITE;
-- Do work, then unlock
UNLOCK TABLES;

Why this works

System tables require separate locking contexts from user tables.

Sources
Official documentation ↗

MySQL 8.0 — 1221 ER_WRONG_LOCK_OF_SYSTEM_TABLE

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