mysql索引优化解决方案

mysql索引优化解决方案(在b站动力节点学习的)

可能因为这个视频是比较新的视频，评论区都没有什么笔记和文档。于是我就跟着视频边学边记录笔记。希望有些建表的代码，有需要的可以直接复制，减少了大家的无效内卷时间，哈哈

# 随表建立索引
create table customer(
 id int(10) auto_increment,
 customer_no varchar(20),
 customer_name varchar(20),
 primary key(id),
 unique indx_customer_no(customer_no),
 key indx_customer_name(customer_name),
 key indx_customer_no_name(customer_no,customer_name)

)

drop table if exists customer;
create table customer(
 id int(10),
 customer_no varchar(20),
 customer_name varchar(20)

)

# 创建主键索引
alter table customer add primary key(id);
# 删除主键索引
alter table customer drop primary key;

# 创建唯一索引
alter table customer add unique idx_customer_no(customer_no);
# 删除唯一索引
drop index idx_customer_no on customer;

# 创建单值索引
alter table customer add index idx_customer_name(customer_name);
# 删除单值索引
drop index idx_customer_name on customer

#创建复合索引
alter table customer add index idx_customer_no_name(customer_no,customer_name);
#删除复合索引
drop index idx_customer_no_name on customer

-- 建表
DROP TABLE IF EXISTS person;
create table person(
PID int (11) auto_increment COMMENT '编号',
PNAME varchar(50) COMMENT '姓名',
PSEX varchar(10) COMMENT '性别',
PAGE int(11) COMMENT '年龄',
SAL decimal(7,2) COMMENT '工资',
primary key(PID)
);

-- 创建存储过程
create procedure insert_person(in max_num int(10))
begin
 declare i int default 0;
 set autocommit = 0;
 repeat
 set i = i+1;
 insert into person (PID,PNAME,PSEX,PAGE,SAL) values (i,concat('test',floor(rand()*10000000)),if(rand()>0.5,'男','女'),
 floor((rand()*100)+10),floor((rand()*19000)+1000));
 until i = max_num
 end repeat;
 commit;
 end;

 -- 调用存储过程
 call insert_person(30000000);

 -- 不使用索引，根据Pname进行查询
 select * from person where PNAME='test7839204'

 -- 给PNAME建立索引
 alter table person add index idx_pname(PNAME);

 -- 使用索引后，根据Pname进行查询
  select * from person where PNAME='test7839204'

  EXPLAIN select * from person where PNAME='test7839204';
	EXPLAIN select * from person where PID='2800000'

-- 创建四张测试表
create table t1(
   id int(10) auto_increment,
	 content varchar(100),
	 primary key(id)
);
create table t2(
   id int(10) auto_increment,
	 content varchar(100),
	 primary key(id)
);
create table t3(
   id int(10) auto_increment,
	 content varchar(100),
	 primary key(id)
);
create table t4(
   id int(10) auto_increment,
	 content varchar(100),
	 primary key(id)
);

-- 每张表中添加一条数据
 insert into t1(content) values(concat('t1_',floor(1+rand()*1000)));
 insert into t2(content) values(concat('t2_',floor(1+rand()*1000)));
 insert into t3(content) values(concat('t3_',floor(1+rand()*1000)));
 insert into t4(content) values(concat('t4_',floor(1+rand()*1000)));

 #id相同时，执行顺序是从上往下

 EXPLAIN select * from t1,t2,t3 where t1.id=t2.id and t2.id=t3.id;

 #id不同时

 explain select t1.id from t1 where t1.id in
 (select t2.id from t2 where t2.id in
 (select t3.id from t3 where t3.id =1)
 );

 #id相同和id不同
 EXPLAIN select t2.* from t2,(select * from t3) s3 where s3.id =t2.id;

 -- select_type
 EXPLAIN select * from t1  -- SIMPLE简单类型查询

 EXPLAIN select * from (select t1.content from t1) as s1 -- DERIVED是在form列表中包含的子查询被标记成为DERIVED，mysq会递归执行这些子查询，把结果放在临时表里。

 EXPLAIN select t2.* from t2 where t2.id =(select t3.id from t3);

 -- type
 #ALL
 EXPLAIN select * from t1 where t1.content = 'abc';

 #system
 EXPLAIN select * from (select t1.id from t1 where id =1) t

 #const 索引一次就找到了
 EXPLAIN select * from t1 where id =1;

 #eq_ref
 EXPLAIN select t1.*,t2.*
 from t1
 join t2
 on t1.id=t2.id

 #ref非唯一索引扫描
 EXPLAIN select * from t1 where t1.content = 'abc';
 alter table t1 add index idx_t1_content(content)

 #range
 EXPLAIN select * from t2 where t2.id>0;

 #index
 EXPLAIN select * from t1

-- 创建员工表
drop table if exists emps;
create table emps(
  id int PRIMARY KEY AUTO_INCREMENT COMMENT '主键id',
	name varchar (24) COMMENT '姓名',
	age int COMMENT '年龄',
	job varchar (20) COMMENT '职位'
);

insert into emps(name,age,job) values('zhangsan',22,'manager');
insert into emps(name,age,job) values('lisi',23,'cleark');
insert into emps(name,age,job) values('wangwu',24,'salsman');
insert into emps(name,age,job) values('赵六',23,'salsman');

-- extra
-- using filesort 排序时没有使用索引 这个效率比较低
explain select * from emps order by age;

-- using temporary 分组时没有使用索引
explain select COUNT(*),job from emps group by job

-- using index
EXPLAIN select id from emps

-- using whrer
EXPLAIN select id from emps where id >2

-- 创建学生表
create table students(
 id int primary key auto_increment comment '主键id',
 sname varchar(24) comment '学生姓名',
 age int comment '年龄',
 score int comment '分数',
 time TIMESTAMP comment '入学时间'
 );

 insert into students(sname,age,score,time) VALUES('小明',22,100,now());
 insert into students(sname,age,score,time) VALUES('小红',23,80,now());
 insert into students(sname,age,score,time) VALUES('小绿',24,80,now());
 insert into students(sname,age,score,time) VALUES('黑',23,70,now());

 alter table students add index idx_sname_age_score(sname,age,score);

 -- 索引失效情况
 -- 第一种索引失效(复合索引不遵循最左匹配原则)
 EXPLAIN select * from students where sname='小明' and age =22 and score=100;
 EXPLAIN select * from students where sname='小明' and age =22 ; -- key_len 数量越大表明索引使用更充分
 EXPLAIN select * from students where sname='小明'
 EXPLAIN select * from students where sname='小明' and score=100; -- 最左匹配原则，不遵循所以和上面一条语句索引使用率一样

 -- 第二种失效情况(不准在索引列上做任何计算，函数操作，会导致索引失效而转向全表扫描)
 EXPLAIN select * from students where left(sname,2)='小明'

 -- 第三种失效情况(存储引擎不能使用索引中范围条件右边的列)
 EXPLAIN select * from students where sname='小明' and age >22 and score=100;

 -- 第四种失效情况(mysql在使用不等于时无法使用索引会导致全表扫描)
 EXPLAIN select * from students where sname='小明' and age =22 and score!=100;

 -- 第五种失效情况(isnull 可以使用索引，但是is not null无法使用索引)
 EXPLAIN select * from students where sname is not null;

 -- 第六种失效情况(like以通配符开头会使索引失效导致全表扫描)
 EXPLAIN select * from students where sname like '% %';

 -- 第七种失效情况(字符串不加单引号索引会失效)
 EXPLAIN select * from students where sname =123

 -- 第八种失效情况(使用or连接时索引会失效)
 EXPLAIN select * from students where sname='小明' or age =22

 -- 单表优化查询优化
 create table if not exists article(
    id int(10) primary key AUTO_INCREMENT,
		author_id int(10) not null,
		category_id int(10) not null,
		views int(10) not null,
		comments int(10) not null,
		title VARBINARY(255) not null,
		content TEXT not null
 );

 insert into article(author_id,category_id,views,comments,title,content)
 VALUES
 (1,1,1,1,'1','1'),
 (2,2,2,2,'2','2'),
 (1,1,3,3,'3','3');

 #1.查询category_id为1的，且comments大于1的情况下，views最多的id和author_id的信息
 EXPLAIN select id,author_id from article where category_id=1 and comments>1 ORDER BY views desc limit 1;
 #2.建立索引
 alter table article add index index_category_id_comments_views(category_id,comments,views)
 #3.再次测试
 EXPLAIN select id,author_id from article where category_id=1 and comments>1 ORDER BY views desc limit 1;
 #4.重新创建索引
 drop index index_category_id_comments_views on article
 alter table article add index index_category_views(category_id,views)
 #5.再次测试
 EXPLAIN select id,author_id from article where category_id=1 and comments>1 ORDER BY views desc limit 1;

 -- 关联查询优化
 create table if not exists class(
   id int(10) auto_increment,
	 card int(10),
	 primary key(id)
 );
  create table if not exists book(
   bookid int(10) auto_increment,
	 card int(10),
	 primary key(bookid)
 );

 #class表
 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)));

 #book表
 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)));

  #1.联表查询
 EXPLAIN select *
 from class
 left join book
 on class.card=book.card;
 #2.建立索引
 alter table book add index indx_card(card)
 #3.测试
 EXPLAIN select *
 from class
 left join book
 on class.card=book.card;

 -- 分组优化

 EXPLAIN select count(*),sname from students
 where sname='小明' and age>22
 GROUP BY score
 alter table students add index idx_sas1(sname,score);
 drop index idx_sas1 on students

 -- 慢查询日志
 -- 查看是否开启
 show variables like '%slow_query_log%'

 -- 开启日志:set global slow_query_log=1;
 set global slow_query_log=1;

 -- 设置时间:set global long_query_time=1;
 set global long_query_time=3;

 -- 查看时间:show variables like 'long_query_time%'
 show variables like 'long_query_time%';

 -- 关闭慢查询日志
 set global slow_query_log=0

学习心得

花了一个上午的时间认真的学习了一遍，感觉收获比较深刻，之前自己项目里面的代码有的sql执行了几秒钟，一直没有优化，现在学完之后知道怎么去优化sql，挺有成就感的，加油。各位