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create table t1(a int primary key , b int , c int, index(b,c));
insert into t1 values(1,1,1),(2,2,2),(3,3,3),(4,4,4),(5,5,5);
insert into t1 select a+5, b+5, c+5 from t1;
insert into t1 select a+10, b+10, c+10 from t1;
insert into t1 select a+20, b+20, c+20 from t1;
insert into t1 select a+40, b+40, c+40 from t1;
explain select * from t1 where a=34;;
id 1
select_type SIMPLE
table t1
type const
possible_keys PRIMARY
key PRIMARY
key_len 4
ref const
rows 1
Extra
explain select * from t1 where b=34 and c = 34;;
id 1
select_type SIMPLE
table t1
type ref
possible_keys b
key b
key_len 10
ref const,const
rows 1
Extra
explain select * from t1 where c=34;;
id 1
select_type SIMPLE
table t1
type ALL
possible_keys NULL
key NULL
key_len NULL
ref NULL
rows 80
Extra Using where
drop table t1;
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