drop table if exists t1; SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=4, SQL_MAX_JOIN_SIZE=9; create table t1 (a int auto_increment primary key, b char(20)); insert into t1 values(1,"test"); SELECT SQL_BUFFER_RESULT * from t1; a b 1 test update t1 set b="a" where a=1; delete from t1 where a=1; insert into t1 values(1,"test"),(2,"test2"); SELECT SQL_BUFFER_RESULT * from t1; a b 1 test 2 test2 update t1 set b="a" where a=1; select 1 from t1,t1 as t2,t1 as t3; 1 1 1 1 1 update t1 set b="a"; You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column update t1 set b="a" where b="test"; You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column delete from t1; You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column delete from t1 where b="test"; You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column delete from t1 where a+0=1; You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column select 1 from t1,t1 as t2,t1 as t3,t1 as t4,t1 as t5; The SELECT would examine more rows than MAX_JOIN_SIZE. Check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is ok update t1 set b="a" limit 1; update t1 set b="a" where b="b" limit 2; delete from t1 where b="test" limit 1; delete from t1 where a+0=1 limit 2; alter table t1 add key b (b); SET MAX_JOIN_SIZE=2; SELECT @@MAX_JOIN_SIZE, @@SQL_BIG_SELECTS; @@max_join_size @@sql_big_selects 2 0 insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"); SELECT * from t1 order by a; The SELECT would examine more rows than MAX_JOIN_SIZE. Check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is ok SET SQL_BIG_SELECTS=1; SELECT * from t1 order by a; a b 2 test2 3 a 4 a 5 a SET MAX_JOIN_SIZE=2; SELECT * from t1; The SELECT would examine more rows than MAX_JOIN_SIZE. Check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is ok SET MAX_JOIN_SIZE=DEFAULT; SELECT * from t1; a b 2 test2 3 a 4 a 5 a SELECT @@MAX_SEEKS_FOR_KEY; @@max_seeks_for_key 4294967295 analyze table t1; Table Op Msg_type Msg_text test.t1 analyze status OK insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"); explain select * from t1,t1 as t2 where t1.b=t2.b; table type possible_keys key key_len ref rows Extra t1 ALL b NULL NULL NULL 21 t2 ALL b NULL NULL NULL 16 Using where set MAX_SEEKS_FOR_KEY=1; explain select * from t1,t1 as t2 where t1.b=t2.b; table type possible_keys key key_len ref rows Extra t1 ALL b NULL NULL NULL 21 t2 ref b b 21 t1.b 6 Using where SET MAX_SEEKS_FOR_KEY=DEFAULT; drop table t1; SET SQL_SAFE_UPDATES=0,SQL_SELECT_LIMIT=DEFAULT, SQL_MAX_JOIN_SIZE=DEFAULT;