select * from t0,t1 where (t0.key1=t1.key1) and ( t0.key1=3 or t0.key2=4);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 index_merge i1,i2 i1,i2 4,4 NULL # Using union(i1,i2); Using where
1 SIMPLE t1 ref i1 i1 4 test.t0.key1 #
explain
select * from t0,t1 where (t0.key1=t1.key1) and
(t0.key1=3 or t0.key2=4) and t1.key1<200;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 # i1,i2 # # test.t0.key1 # #
1 SIMPLE t1 # i1 # # test.t0.key1 # #
explain
select * from t0,t1 where (t0.key1=t1.key1) and
(t0.key1=3 or t0.key2<4) and t1.key1=2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ref i1,i2 i1 4 test.t0.key1 # Using where
1 SIMPLE t1 ref i1 i1 4 test.t0.key1 #
explain select * from t0,t1 where t0.key1 = 5 and
(t1.key1 = t0.key1 or t1.key8 = t0.key1);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ref i1 i1 4 test.t0.key1 #
1 SIMPLE t1 index_merge i1,i8 i1,i8 4,4 test.t0.key1 # Using union(i1,i8); Using where; Using join buffer
explain select * from t0,t1 where t0.key1 < 3 and
(t1.key1 = t0.key1 or t1.key8 = t0.key1);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 range i1 i1 4 test.t0.key1 # Using where
1 SIMPLE t1 ALL i1,i8 NULL NULL test.t0.key1 # Range checked for each record (index map: 0x81)
explain select * from t1 where key1=3 or key2=4
union select * from t1 where key1<4 or key3=5;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 index_merge i1,i2 i1,i2 4,4 NULL # Using union(i1,i2); Using where
2 UNION t1 index_merge i1,i3 i1,i3 4,4 NULL # Using sort_union(i1,i3); Using where
NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL #
explain select * from (select * from t1 where key1 = 3 or key2 =3) as Z where key8 >5;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> system NULL NULL NULL NULL #
2 DERIVED t1 index_merge i1,i2 i1,i2 4,4 NULL # Using union(i1,i2); Using where; Using index
create table t3 like t0;
insert into t3 select * from t0;
alter table t3 add key9 int not null, add index i9(key9);
alter table t3 add keyA int not null, add index iA(keyA);
alter table t3 add keyB int not null, add index iB(keyB);
alter table t3 add keyC int not null, add index iC(keyC);
update t3 set key9=key1,keyA=key1,keyB=key1,keyC=key1;
explain select * from t3 where
key1=1 or key2=2 or key3=3 or key4=4 or
key5=5 or key6=6 or key7=7 or key8=8 or
key9=9 or keyA=10 or keyB=11 or keyC=12;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 index_merge i1,i2,i3,i4,i5,i6,i7,i8,i9,iA,iB,iC i1,i2,i3,i4,i5,i6,i7,i8,i9,iA,iB,iC 4,4,4,4,4,4,4,4,4,4,4,4 NULL # Using union(i1,i2,i3,i4,i5,i6,i7,i8,i9,iA,iB,iC); Using where
explain select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge key1,key2,key3,key4 key3,key1,key2,key4 5,5,5,5 NULL # Using union(key3,intersect(key1,key2),key4); Using where
select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
key1 key2 key3 key4 filler1
100 100 200 200 key1-key2-key3-key4-1
100 100 200 200 key1-key2-key3-key4-2
100 100 200 200 key1-key2-key3-key4-3
-1 -1 -1 200 key4
-1 -1 200 -1 key3
explain select * from t1 where st_a=1 and st_b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b # 4 const # Using where
explain select st_a,st_b from t1 where st_a=1 and st_b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b st_a,st_b 4,4 NULL # Using intersect(st_a,st_b); Using where; Using index
explain select st_a from t1 ignore index (st_a) where st_a=1 and st_b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,stb_swt1a_2b,stb_swt1b,st_b # 4 const # Using where
explain select * from t1 where st_a=1 and swt1a=1 and swt2a=1;
id select_type table type possible_keys key key_len ref rows Extra
explain select * from t1 where st_b=1 and swt1b=1 and swt2b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref stb_swt1a_2b,stb_swt1b,st_b stb_swt1a_2b 8 const,const # Using where
explain select * from t1 where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b sta_swt12a,stb_swt1a_2b 12,12 NULL # Using intersect(sta_swt12a,stb_swt1a_2b); Using where
explain select * from t1 ignore index (sta_swt21a, stb_swt1a_2b)
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,st_a,stb_swt1b,st_b sta_swt12a,stb_swt1b 12,8 NULL # Using intersect(sta_swt12a,stb_swt1b); Using where
explain select * from t1 ignore index (sta_swt21a, sta_swt12a, stb_swt1a_2b)
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt1a,sta_swt2a,st_a,stb_swt1b,st_b sta_swt1a,sta_swt2a,stb_swt1b 8,8,8 NULL # Using intersect(sta_swt1a,sta_swt2a,stb_swt1b); Using where
explain select * from t1 ignore index (sta_swt21a, sta_swt12a, stb_swt1a_2b, stb_swt1b)
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt1a,sta_swt2a,st_a,st_b sta_swt1a,sta_swt2a,st_b 8,8,4 NULL # Using intersect(sta_swt1a,sta_swt2a,st_b); Using where
explain select * from t1
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b sta_swt12a,stb_swt1a_2b 12,12 NULL # Using intersect(sta_swt12a,stb_swt1a_2b); Using where
explain select * from t1
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b sta_swt1a,stb_swt1b 8,8 NULL # Using intersect(sta_swt1a,stb_swt1b); Using where
explain select st_a from t1
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b sta_swt1a,stb_swt1b 8,8 NULL # Using intersect(sta_swt1a,stb_swt1b); Using where; Using index
explain select st_a from t1
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b sta_swt1a,stb_swt1b 8,8 NULL # Using intersect(sta_swt1a,stb_swt1b); Using where; Using index
drop table t0,t1;
create table t2 (
a char(10),
b char(10),
filler1 char(255),
filler2 char(255),
key(a(5)),
key(b(5))
);
select count(a) from t2 where a='BBBBBBBB';
count(a)
4
select count(a) from t2 where b='BBBBBBBB';
count(a)
4
expla_or_bin select count(a_or_b) from t2 where a_or_b='AAAAAAAA' a_or_bnd a_or_b='AAAAAAAA';
id select_type ta_or_ba_or_ble type possia_or_ble_keys key key_len ref rows Extra_or_b
1 SIMPLE t2 ref a_or_b,a_or_b a_or_b 6 const 4 Using where
select count(a) from t2 where a='AAAAAAAA' and b='AAAAAAAA';
count(a)
4
select count(a) from t2 ignore index(a,b) where a='AAAAAAAA' and b='AAAAAAAA';
count(a)
4
insert into t2 values ('ab', 'ab', 'uh', 'oh');
explain select a from t2 where a='ab';
id select_type table type possible_keys key key_len ref rows Extra