MySQL優化索引之雙表優化

2021-10-05 17:55:36 字數 3593 閱讀 4216

建表sql

create table if not exists `class`(


`id` int(10) unsigned not null primary key auto_increment,


`card` int (10) unsigned not null); 


create table if not exists `book`(


`bookid` int(10) unsigned not null primary key auto_increment,


`card` int (10) unsigned not null); 


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into class(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));


insert into book(card)values(floor(1+(rand()*20)));
需求1：兩張表左連線，即要左表的全部資料+左右共有部分不加索引的情況下左右表查詢都是all 

要想優化左連線，要在右表加索引

alter table `book` add index y ( `card` );
再次檢視執行計畫

需求2：兩張表右連線，即要右表的全部資料+左右共有部分要想優化右連線，要在左表加索引

先刪除上一步的右表索引

drop index y on book;
然後在左表上建立索引

alter table class add index y (card);
再次執行查詢計畫 

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