drop table if exists t1,t2; create table t1(a int, unique(a)); insert into t1 values(2); create table t2(a int); insert into t2 values(1),(2); reset master; insert into t1 select * from t2; ERROR 23000: Duplicate entry '2' for key 'a' source include/show_binlog_events.inc; Log_name Pos Event_type Server_id End_log_pos Info master-bin.000001 # Table_map # # table_id: # (test.t1) master-bin.000001 # Write_rows # # table_id: # flags: STMT_END_F select * from t1; a 1 2 drop table t1, t2; create table t1(a int); insert into t1 values(1),(1); reset master; create table t2(unique(a)) select a from t1; ERROR 23000: Duplicate entry '1' for key 'a' source include/show_binlog_events.inc; Log_name Pos Event_type Server_id End_log_pos Info drop table t1;