ERROR 1062 (23000): Duplicate entry for key 'PRIMARY'

ALTER TABLE table1 ADD COLUMN column1 VARCHAR(400) DEFAULT NULL; ERROR 1062 (23000): Duplicate entry '82133627' for key 'PRIMARY' select * from table1 where <primary_key_field>='82133627'; Primary key - primary_key_field int(11) NOT NULL solution - need to lock table, and then after running the query unlock it LOCK TABLES "table1" WRITE; run the alter table command： ALTER TABLE table1 ADD COLUMN column1 VARCHAR(400) DEFAULT NULL; then UNLOCK TABLES;