You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 

89 lines
4.0 KiB

drop table if exists t1;
create table t1 (id int not null, str char(10), unique(str));
explain select * from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system NULL NULL NULL NULL 0 const row not found
insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
select * from t1 where str is null;
id str
1 NULL
2 NULL
select * from t1 where str="foo";
id str
3 foo
explain select * from t1 where str is null;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref str str 11 const 1 Using where
explain select * from t1 where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const str str 11 const 1
explain select * from t1 ignore key (str) where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using where
explain select * from t1 use key (str,str) where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const str str 11 const 1
explain select * from t1 use key (str,str,foo) where str="foo";
ERROR 42000: Key 'foo' doesn't exist in table 't1'
explain select * from t1 ignore key (str,str,foo) where str="foo";
ERROR 42000: Key 'foo' doesn't exist in table 't1'
drop table t1;
explain select 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
create table t1 (a int not null);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
insert into t1 values(1);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
insert into t1 values(1);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1;
set names koi8r;
create table ÔÁÂ (ËÏÌ0 int, ËÏÌ1 int, key ÉÎÄ0 (ËÏÌ0), key ÉÎÄ01 (ËÏÌ0,ËÏÌ1));
insert into ÔÁÂ (ËÏÌ0) values (1);
insert into ÔÁÂ (ËÏÌ0) values (2);
explain select ËÏÌ0 from ÔÁÂ where ËÏÌ0=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE ÔÁÂ ref ÉÎÄ0,ÉÎÄ01 ÉÎÄ0 5 const 1 Using where; Using index
drop table ÔÁÂ;
set names latin1;
select 3 into @v1;
explain select 3 into @v1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
create table t1(f1 int, f2 int);
insert into t1 values (1,1);
create view v1 as select * from t1 where f1=1;
explain extended select * from v1 where f2=1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` where 1
explain extended select * from t1 where 0;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 0
explain extended select * from t1 where 1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` where 1
explain extended select * from t1 having 0;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible HAVING
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` having 0
explain extended select * from t1 having 1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` having 1
drop view v1;
drop table t1;