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ab576328f0
to estimate correctly cost of full table scan we should take into account rows read and skipped on each iteration.
82 lines
2.9 KiB
Plaintext
82 lines
2.9 KiB
Plaintext
drop table if exists t1;
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SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=4, SQL_MAX_JOIN_SIZE=9;
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create table t1 (a int auto_increment primary key, b char(20));
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insert into t1 values(1,"test");
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SELECT SQL_BUFFER_RESULT * from t1;
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a b
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1 test
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update t1 set b="a" where a=1;
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delete from t1 where a=1;
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insert into t1 values(1,"test"),(2,"test2");
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SELECT SQL_BUFFER_RESULT * from t1;
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a b
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1 test
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2 test2
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update t1 set b="a" where a=1;
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select 1 from t1,t1 as t2,t1 as t3;
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1
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1
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1
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1
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1
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update t1 set b="a";
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You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
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update t1 set b="a" where b="test";
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You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
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delete from t1;
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You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
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delete from t1 where b="test";
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You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
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delete from t1 where a+0=1;
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You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
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select 1 from t1,t1 as t2,t1 as t3,t1 as t4,t1 as t5;
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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
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update t1 set b="a" limit 1;
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update t1 set b="a" where b="b" limit 2;
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delete from t1 where b="test" limit 1;
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delete from t1 where a+0=1 limit 2;
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alter table t1 add key b (b);
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SET MAX_JOIN_SIZE=2;
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SELECT @@MAX_JOIN_SIZE, @@SQL_BIG_SELECTS;
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@@max_join_size @@sql_big_selects
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2 0
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insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a");
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SELECT * from t1 order by a;
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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
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SET SQL_BIG_SELECTS=1;
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SELECT * from t1 order by a;
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a b
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2 test2
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3 a
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4 a
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5 a
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SET MAX_JOIN_SIZE=2;
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SELECT * from t1;
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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
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SET MAX_JOIN_SIZE=DEFAULT;
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SELECT * from t1;
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a b
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2 test2
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3 a
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4 a
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5 a
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SELECT @@MAX_SEEKS_FOR_KEY;
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@@max_seeks_for_key
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4294967295
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analyze table t1;
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Table Op Msg_type Msg_text
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test.t1 analyze status OK
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insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a");
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explain select STRAIGHT_JOIN * from t1,t1 as t2 where t1.b=t2.b;
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table type possible_keys key key_len ref rows Extra
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t1 ALL b NULL NULL NULL 21
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t2 ref b b 21 t1.b 6 Using where
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set MAX_SEEKS_FOR_KEY=1;
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explain select STRAIGHT_JOIN * from t1,t1 as t2 where t1.b=t2.b;
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table type possible_keys key key_len ref rows Extra
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t1 ALL b NULL NULL NULL 21
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t2 ref b b 21 t1.b 6 Using where
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SET MAX_SEEKS_FOR_KEY=DEFAULT;
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drop table t1;
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SET SQL_SAFE_UPDATES=0,SQL_SELECT_LIMIT=DEFAULT, SQL_MAX_JOIN_SIZE=DEFAULT;
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