數(shù)據(jù)庫day06-索引和執(zhí)行計劃管理

第四章索引及執(zhí)行計劃管理

資料-索引及執(zhí)行計劃

1. 索引的作用

類似于一本書的目錄,起到優(yōu)化查詢的功能

2. 索引類型(筆試)

BTREE索引 *****

RTREE索引

HASH索引

全文索引

3. BTREE的細(xì)分離(算法)

B-TREE渣淳，B+TREE，B*TREE 原理圖提取碼: p1h5

B-TREE

B+TREE

B*TREE

4. Btree索引的功能分類

聚集索引(集群索引) *****

輔助索引(二級索引)

5.B樹是如何構(gòu)建的

輔助索引

alter table t1 add index idx_name(name);

1.將name列的所有值取出來猖任，進行自動排序
2.將排完序的值均勻的落到16KB葉子節(jié)點數(shù)據(jù)頁中尺上，并將索引鍵值所對應(yīng)的數(shù)據(jù)行的幾句索引列值
3.向上生成枝節(jié)點和根節(jié)點

聚集索引(IOT)

1.默認(rèn)是按照主鍵生成聚集索引金顿，沒有主鍵，存儲引擎會使用唯一鍵贰您。
  如果都沒有坏平，會自動生成隱藏的聚集索引
2.數(shù)據(jù)在存儲時，就會按照聚集索引打的順序存儲到磁盤的數(shù)據(jù)頁
3.由于本身書籍就是有序的锦亦，所以聚集索引構(gòu)建時舶替，不需要進行排序
4.聚集索引直接將磁盤的數(shù)據(jù)頁，作為葉子節(jié)點
5.枝節(jié)點和根節(jié)點只會調(diào)取下層節(jié)點主鍵的最小值

6. 輔助索引和聚集索引區(qū)別

(1) 輔助索引：
  葉子節(jié)點只保存主鍵值+索引鍵值的有序存儲
  對索引鍵值會知道排序
  需要手工創(chuàng)建
  輔助索引可以有多個
  任何列都可以創(chuàng)建
(2) 
  只能在主鍵列生成杠园，唯一且非空
  數(shù)據(jù)存儲時顾瞪，就是按照聚集索引順序進行有序存儲
  葉子節(jié)點保存的是整個有序的數(shù)據(jù)行
  葉子節(jié)點不需要單獨生成

7. 輔助索引細(xì)分

7.1 單列輔助索引

select * from t1 where name=''

7.2 聯(lián)合索引

select * from t1 where a and b and c

7.3唯一索引

8.索引樹的高度(越低越好)

1. 表的數(shù)據(jù)量級大

分區(qū)表

分庫分表(分布式架構(gòu))

2. 列的長度

盡可能選擇列值短的創(chuàng)建索引

采用前綴索引

3. 數(shù)據(jù)類型選擇

varchar 和 char

enum

9.索引管理

9.1 壓力測試準(zhǔn)備

create database test charset utf8mb4;
use test;
create table t100w (id int,num int,k1 char(2),k2 char(4),dt timestamp);
delimiter //
create  procedure rand_data(in num int)
begin
declare str char(62) default 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
declare str2 char(2);
declare str4 char(4);
declare i int default 0;
while i<num do
set str2=concat(substring(str,1+floor(rand()*61),1),substring(str,1+floor(rand()*61),1));
set str4=concat(substring(str,1+floor(rand()*61),2),substring(str,1+floor(rand()*61),2));
set i=i+1;
insert into t100w values (i,floor(rand()*num),str2,str4,now());
end while;
end;
//
delimiter ;

插入100w條數(shù)據(jù)：

call rand_data(1000000);

commit;

MySQL [test]>select count(*) from t100w;
+----------+
| count(*) |
+----------+
|  1000000 |
+----------+
1 row in set (0.47 sec)

9.2 索引命令操作

查詢索引

use school
show tables;
desc student;

Key : PRI（主鍵），UNI（唯一索引）抛蚁，MUL（輔助索引）

show index from student\G

創(chuàng)建單列索引

alter table student add index idx_name(sname);

創(chuàng)建聯(lián)合索引

alter table student add index idx_sname_sage_ssex(sname,sage,ssex);

idx_a_b_c -----> idx_a   idx_a_b   idx_a_b_c

創(chuàng)建前綴索引

alter table student add index idx(sname(5));

alter table student add telnum char(11) not null;

創(chuàng)建唯一索引

mysql[school]>alter table student add telnum char(11) not null ;
mysql[school]>alter table student add unique index idx_tel(telnum);

# 判斷某個列有或沒有重復(fù)值
MySQL [world]>select name,count(id) from city group by name having count(id)>1 order by count(id) desc ;
+---------------+-----------+
| name          | count(id) |
+---------------+-----------+
| San José      |         4 |
| Córdoba       |         3 |
| Springfield   |         3 |
...
.....
| Brest         |         2 |
| Manchester    |         2 |
| Santa Maria   |         2 |
| Colombo       |         2 |
| San Carlos    |         2 |

| Jinzhou       |         2 |
+---------------+-----------+
67 rows in set (0.00 sec)

MySQL [world]>select count(*) from city;
+----------+
| count(*) |
+----------+
|     4079 |
+----------+
1 row in set (0.00 sec)

MySQL [world]>select count(distinct name) from city;
+----------------------+
| count(distinct name) |
+----------------------+
|                 3998 |
+----------------------+
1 row in set (0.00 sec)

刪除索引

mysql[school]>alter table student drop index idx;
mysql[school]>alter table student drop index idx_name;
mysql[school]>alter table student drop index idx_sname_sage_ssex;

9.3沒有索引和添加索引的差別

mysqlslap --defaults-file=/etc/my.cnf --concurrency=100 --iterations=1 --create-schema='test' --query="select * from test.t100w where k2='VWtu'" engine=innodb --number-of-queries=2000 -uroot -p123456 -verbose

優(yōu)化前

use test;
show tables;
desc t100w;
alter table t100w add index idx_k2(k2);  #優(yōu)化

優(yōu)化后

10. explain (desc) ☆☆☆☆☆

explain select * from test.t100w where k2='VWtu';
or
desc select * from test.t100w where k2='VWtu';

作用 : 抓取優(yōu)化器優(yōu)化過的執(zhí)行計劃

10.1 執(zhí)行計劃的分析

MySQL [test]>explain select * from test.t100w where k2='VWtu';
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | t100w | NULL       | ref  | idx_k2        | idx_k2 | 17      | const | 1120 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+

重點３滦选！瞧甩！

table：以上SQL語句設(shè)計到的表☆☆☆
type：查詢的類型(全表掃描(ALL)钉跷，索引掃描，查不到數(shù)據(jù)(NULL))☆☆☆☆☆
possible_keys：可能會用到的索引☆☆☆
key：使用到的索引☆☆☆☆
key_len：索引的覆蓋長度☆☆☆☆☆
Extra：額外的信息☆☆☆☆

10.2 type 詳細(xì)說明☆☆☆☆☆

10.2.1 ALL：全表掃描,不走索引

(1) 查詢條件肚逸，沒建索引
>use test;
>MySQL [test]>alter table t100w drop index idx_k2;
>MySQL [test]>explain select * from test.t100w where k2='VWtu';
+----+-------------+-------+------------+------+---------------+------+---------+------+--------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows   | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+--------+----------+-------------+
|  1 | SIMPLE      | t100w | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 937395 |    10.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+--------+----------+-------------+
1 row in set, 1 warning (0.00 sec)


MySQL [test]>desc t100w;
+-------+-----------+------+-----+-------------------+-----------------------------+
| Field | Type      | Null | Key | Default           | Extra                       |
+-------+-----------+------+-----+-------------------+-----------------------------+
| id    | int(11)   | YES  |     | NULL              |                             |
| num   | int(11)   | YES  |     | NULL              |                             |
| k1    | char(2)   | YES  |     | NULL              |                             |
| k2    | char(4)   | YES  |     | NULL              |                             |
| dt    | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------+-----------+------+-----+-------------------+-----------------------------+
5 rows in set (0.00 sec)

(2) 有索引不走
mysql [test]>alter table t100w add index idx_k2(k2);
Query OK, 0 rows affected (3.57 sec)
Records: 0  Duplicates: 0  Warnings: 0

desc select * from t100w where k2 != 'asdf';
desc select * from t100w where k2 like '%aa%';
desc select * from t100w where k2 not in ('asda','asas');
desc select * from t100w;

注意: !=和not in 如果是主鍵列,是走range
mysql[test]>desc select * from world.city where id != 10;
mysql[test]>desc select * from world.city where id not in (10,20);

10.2.2 index 全索引掃描

MySQL [test]>desc select k2 from t100w;

=====從range開始爷辙，我們才認(rèn)為索引是有價值的======

10.2.3 range 索引范圍查詢

所有索引：
>, <, >=, <=, like, between and
mysql[world]>desc select * from city where id<10;
mysql[world]>desc select * from city where countrycode like 'CH%

in () or 
oldguo[world]>desc select * from city where countrycode in ('CHN','USA');

聚集索引：
!= not in
mysql[test]>desc select * from world.city where id != 10;
mysql[test]>desc select * from world.city where id not in (10,20);
========================================

說明：
B+tree 索引能額外優(yōu)化到:> ,<, >=, <= ,like , between and
in 和 or 享受不到b+tree額外的優(yōu)化效果的,所以我一般情況會將in , or 進行改寫
mysql[world]>desc select * from city where countrycode = 'CHN' union all  select * from city where countrycode = 'USA';
+----+-------------+-------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key         | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
|  1 | PRIMARY     | city  | NULL       | ref  | CountryCode   | CountryCode | 3       | const |  363 |   100.00 | NULL  |
|  2 | UNION       | city  | NULL       | ref  | CountryCode   | CountryCode | 3       | const |  274 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)

10.2.4 ref 輔助索引等值查詢

MySQL [world]>desc select * from city where countrycode='CHN';

10.2.5 eq_ref 多表連接查詢中, 非驅(qū)動表的on的調(diào)劑列是主鍵唯一鍵

MySQL [world]>desc select a.name,b.name from city as a join country as b on a.countrycode=b.code where a.population<100;
+----+-------------+-------+------------+--------+---------------+---------+---------+---------------------+------+----------+-------------+
| id | select_type | table | partitions | type   | possible_keys | key     | key_len | ref                 | rows | filtered | Extra       |
+----+-------------+-------+------------+--------+---------------+---------+---------+---------------------+------+----------+-------------+
|  1 | SIMPLE      | a     | NULL       | ALL    | CountryCode   | NULL    | NULL    | NULL                | 4188 |    33.33 | Using where |
|  1 | SIMPLE      | b     | NULL       | eq_ref | PRIMARY       | PRIMARY | 3       | world.a.CountryCode |    1 |   100.00 | NULL        |
+----+-------------+-------+------------+--------+---------------+---------+---------+---------------------+------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

10.2.6 const(system) 主鍵或唯一鍵的等值

MySQL [world]>desc select * from city where id=10;
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | city  | NULL       | const | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

NULL : 獲取不到數(shù)據(jù)
oldguo[world]>desc select * from city where id=100000000000000;

10.3 possible_keys：可能會用到的索引☆ ☆ ☆

NULL：沒有和查詢條件匹配的所有條目
有值：有和查詢條件匹配的索引條目彬坏，但是沒走，大部分原因是語句查詢方式不符合索引應(yīng)用條件

10.4 key：使用到的索引☆☆☆☆

最終使用的索引膝晾，可以幫助我們判斷是否走了合適的索引

10.5 key_len：索引的覆蓋長度☆☆☆☆☆

在聯(lián)合索引應(yīng)用的判斷時苍鲜，會經(jīng)常看

單列索引:

字符集	字節(jié)個數(shù)	not null	沒有指定not null
utf8	3個字節(jié)
int	4個字節(jié)	4	4+1
tinyint	1個字節(jié)	1	2
utf8mb4	一個字符最大是4個字節(jié)
char(2)		2*4	2*4+1
varchar(2)		2*4+2	2*4+2+1

說明：

有非空約束時玷犹，key_length就是最大字節(jié)長度

在沒有非空約束時：字符最大長度+1

varchar類型，需要額外在最大字符長度+2(存儲字符長度的最長度占位)

create table t1 (
id int ,
num int not null, 
k1 char(2),
k2 char(2) not null,
k3 varchar(2),
k4 varchar(2) not null)charset utf8mb4;

聯(lián)合搜索優(yōu)化


MySQL [world]>desc t1;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | YES  |     | NULL    |       |
| num   | int(11)    | NO   |     | NULL    |       |
| k1    | char(2)    | YES  |     | NULL    |       |
| k2    | char(2)    | NO   |     | NULL    |       |
| k3    | varchar(2) | YES  |     | NULL    |       |
| k4    | varchar(2) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+

====================================
alter table t1 add index idx(id,num,k1,k2,k3,k4);
select 5+4+9+8+11+10;  \\ 47

(1)最完美的查詢情況

idx(id,num,k1,k2,k3,k4)
desc select * from t1 where id=1 and num=1 and k1='a' and k2'a' and k3='a' and k4='a';
desc select * from t1 where num=1 and id=1 and k1='a' and k2'a' and k3='a' and k4='a';

結(jié)論：
當(dāng)查詢條件中歹颓，包含了索引列中所有的列條件油湖，并且都是等值的查詢，那么無關(guān)排列順序乏德，都可以走全聯(lián)合索引優(yōu)化撤奸；
原因是優(yōu)化器會自動調(diào)整順序喊括，達到最佳的優(yōu)化效果
所以，我們重點需要關(guān)注的是聯(lián)合索引建立的順序,從左到右郑什，唯一值越多的列放在最左邊

(2) 查詢條件中府喳，哪些因素會key_len長度

#安裝索引的建立順序，在查詢條件中蘑拯，少了任意一個中間列，后續(xù)列都無法走索引
desc select * from t1 where id=1 and k1='a' and k2'a' and k3='a' and k4='a';

#在條件查詢中間,出現(xiàn)不等值查詢時,從不等值列開始,所有列都無法使用聯(lián)合索引 (暫存)
oldguo[world]>desc select * from t1 where  id=1 and num>10 and k1='a' and k2='a' and k3='a' and k4='a';

優(yōu)化方法:

將不等值列放在最后.
oldguo[world]>alter table t1 add index idx1(id,k1,k2,k3,k4,num);
oldguo[world]>alter table t1 drop index idx;

(3) 如果有多子句的條件查詢(必須是聯(lián)合索引)
按照子句的執(zhí)行順序,建立聯(lián)合索引.

10.6 Extra：額外的信息 ☆☆☆☆

Using filesort :  原因是 在 group  by ,order by,distinct等.
一般優(yōu)化的方法是,和where條件的列建立聯(lián)合索引

11.小結(jié)

11.1 索引的類型(算法)

BTree
HASH
RTREE

11.2 BTREE

B-tree
B+TREE  #在葉子節(jié)點加了雙向指針
B*TREE  #在枝節(jié)點加了雙向指針

11.3 B+Tree有什么優(yōu)勢

在葉子節(jié)點增加了相鄰葉子節(jié)點雙向指針
為了優(yōu)化范圍查詢

11.4 輔助索引和聚集索引區(qū)別

葉子節(jié)點 ☆☆☆☆☆

輔助索引是手工創(chuàng)建的弯蚜，

聚集索引是自動跟主鍵生成

聚集索引只有一個

輔助索引可以有多個

11.5 輔助索引細(xì)分

單列
聯(lián)合
唯一
前綴

11.6 索引樹高度

數(shù)據(jù)量
數(shù)據(jù)類型
數(shù)據(jù)列的長度
聚集索引列的長度

11.7 索引基本管理

show index from t1;
desc t1;
alter table t1 add idnex 索引名(列名)
alter table t1 drop index 索引名

11.8 explain

1. 作用

獲取優(yōu)化器選擇的執(zhí)行計劃

2. 分析執(zhí)行計劃

type :
ALL:全表掃描

(1) 查詢條件沒有建索引
use test
desc select * from t100w where id=10;

(2) 有索引不走
desc select * from t100w where k2 !='aaaa';
desc select * from t100w where k2 like '%aa%';  #前面不加%走索引
desc select * from t100w where k2 not in ('aaaa','bbbb');
desc select * from t100w;  #查全表也不走索引

index:全索引掃描

desc select k2 from t100w;

Range: 索引范圍掃描

#>, <, >=, <=, like, between and
desc select * from world.city where id > 10;

or in 
desc select * from world.city where countrycode in ('CHN','USA');
改寫:
desc select * from world.city where countrycode='CHN' union all
select * from world.city where countrycode='USA';

ref : 輔助索引等值查詢

oldguo[test]>desc select * from world.city where countrycode='CHN';

eq_ref : 多表連接查詢,非驅(qū)動表on的條件列是主鍵或者唯一鍵

 desc select city.name,country.name from city left join country on city.countrycode=country.code where city.population<100;

const(system) : 主鍵或者唯一鍵的等值查詢

oldguo[world]>desc select * from city where id=10;

NULL:略

key_len: utf8mb4

            not null       沒設(shè)置
int            4              +1
varchar(10)    4*10+2         +1
char(10)       4*10           +1

====================================

聯(lián)合索引準(zhǔn)備

create table t1(a int not null ,b char(10) not null ,c varchar(10) not null )charset utf8mb4;
oldguo[test]>desc t1;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| a     | int(11)     | NO   |     | NULL    |       |
| b     | char(10)    | NO   |     | NULL    |       |
| c     | varchar(10) | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

idx(a,b,c) =  4 + 40 + 42 = 86

(1) 最理想的 
desc select * from t1 where a=1 and b='a' and c='a';
desc select * from t1 where b='1' and a=1 and c='a';
desc select * from t1 where c='1' and a=1 and b='a';
desc select * from t1 where c='1' and b='a' and a=1;
desc select * from t1 where a=1 and c='a' and b='a';
desc select * from t1 where b='1' and c='a' and a=1;

唯一值多的放在左邊

(2) 部分索引
desc select * from t1 where a=1 and c='a';
oldguo[test]>desc select * from t1 where a=1 and b like 'a%' and c='a';

(3) where  + order by
Extra:filesort  ===> 排序不走索引,走的額外排序
oldguo[test]>desc select * from world.city where countrycode='CHN' order by population;

擴展:
oldguo[test]>desc format=json select * from t1 where a=1 and c='a' and b='a';