B+-Tree

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16KB

6条数据一组

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select version();

drop table t1;

create table t1 (
	a int primary key,
	b int,
	c int,
	d int,
	e varchar(20)
) engine=InnoDB;

show index from t1;

insert into t1 value (4,3,1,1,'d');
insert into t1 value (1,1,1,1,'a');
insert into t1 value (8,8,8,8,'h');
insert into t1 value (2,2,2,2,'b');
insert into t1 value (5,2,3,5,'e');
insert into t1 value (3,3,2,2,'c');
insert into t1 value (7,4,5,5,'g');
insert into t1 value (6,6,4,4,'f');

create index idx_ti_bcd on t1(b,c,d);
create index idx_ti_e on t1(e);

explain select * from t1 where a + 1 = 1;
explain select * from t1 where a = 1;
explain select * from t1 where a = '1';
explain select * from t1 where e = 1;
explain select * from t1 where e = '1';

select 0=0; -- 1
select 0='a'; -- 1 
select 0='1'; -- 0

explain select * from t1 where b = 1 and c = 1 and d = 1;

explain select * from t1 where c = 1 and d = 1; 

explain select * from t1 where b = 1 and d = 1;

# 查询优化器  全表扫描
explain select * from t1 where b > 1; 

explain select d,c,d,a from t1 where b > 1;

explain select d,c,d,a from t1;

explain select * from t1 where b > 6;