sql优化练习

最新原文：https://www.cnblogs.com/uncleyong/p/14805395.html

单表

create table stu
(
	sid int(4) primary key,
	sname varchar(20) not null,
	phone int(11) not null,
	addr varchar(20) not null,
	class_id int(4) not null,
	grade_id int(4) not null
);

　

explain select sid from stu where grade_id in(2,3) and class_id=1 order by grade_id desc ;

根据上面explain的结果，对sql进行优化

https://www.cnblogs.com/uncleyong/p/14814185.html

 

多表

最新原文：https://www.cnblogs.com/uncleyong/p/14805395.html