# -

> +XMind8 **** 

![-](http://my-blog-to-use.oss-cn-beijing.aliyuncs.com/18-10-2/70973487.jpg)

> ****

# 

> 
>   https://juejin.im/post/5b55b842f265da0f9e589e79
>   Java3y

###  MySQL 

MySQL()

![MySQL](http://my-blog-to-use.oss-cn-beijing.aliyuncs.com/18-10-2/28559421.jpg)

![](http://my-blog-to-use.oss-cn-beijing.aliyuncs.com/18-10-2/82053134.jpg)

 - ****
 -   ****
       - 
       - ()

select * from user where indexname = 'xxx'sql

1. ****
2. ****

On


### 

()

![](http://my-blog-to-use.oss-cn-beijing.aliyuncs.com/18-10-2/5373082.jpg)

id8

![](http://my-blog-to-use.oss-cn-beijing.aliyuncs.com/18-10-2/89338047.jpg)

 **** O(logn)

B+B+

# 

> Java


### 

MySQLUsernamecity(name,city)        

```                                                                                       
select * from user where name=xx and city=xx ; 
select * from user where name=xx ; // 
select * from user where city=xx ; //             
```                                                          
 `city= xx and name xx`

ORDER BY

### 

   name,city name  

MySQL 5.7  sys  `schema_redundant_indexes`              

### Mysql

1.PRIMARY KEY

```
ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` ) 
```
2.UNIQUE() 

```
ALTER TABLE `table_name` ADD UNIQUE ( `column` ) 
```
 
3.INDEX() 

```
ALTER TABLE `table_name` ADD INDEX index_name ( `column` )
```
 
4.FULLTEXT() 

```
ALTER TABLE `table_name` ADD FULLTEXT ( `column`) 
```
 
5.

```
ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` )
```


# 

- Java
- MySQL_3
- https://juejin.im/post/5b55b842f265da0f9e589e79