mysql之Sql优化当建立了索引列后，能在wherel条件中使用索引的尽量所用。如果索引了多列，要遵守最左前缀法则。

Sql优化

策略1.尽量全值匹配

当建立了索引列后，能在wherel条件中使用索引的尽量所用。

CREATE TABLE `staffs`(
	id int primary key auto_increment,
	name varchar(24) not null default "" comment'姓名',
	age int not null default 0 comment '年龄',
	pos varchar(20) not null default ""  comment'职位',
	add_time timestamp not null default current_timestamp comment '入职时间'
	)charset utf8 comment '员工记录表';
 
	
insert into staffs(name,age,pos,add_time) values('z3',22,'manage',now());
insert into staffs(name,age,pos,add_time) values('july',23,'dev',now());
insert into staffs(name,age,pos,add_time) values('2000',23,'dev',now());
 
alter table staffs add index idx_staffs_nameAgePos(name,age,pos);


EXPLAIN SELECT * FROM staffs WHERE NAME = 'July';
EXPLAIN SELECT * FROM staffs WHERE NAME = 'July' AND age = 25;
EXPLAIN SELECT * FROM staffs WHERE NAME = 'July' AND age = 25 AND pos = 'dev';