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;