MySQL use index

 

MySQL Index Overview

• Index is an ordered structure of the database will be the value of the single or multiple columns
• Query data through the index can improve query speed, but also reduce the load on the server

MySQL Index Classification

• Ordinary index ( without applying any constraints index, can be created in any data type )
• Unique index ( value of the index must be unique )
• Full-text index ( created only in char , VARCHAR or text on the types of fields )
• Single index ( only one field corresponding to the index )
• Multi-column index ( create an index on multiple fields of the table )
• Space Index ( can only be established on the spatial data types )

Creating an index

语法:

create  table  table_name

(

    属性名 数据类型[约束条件]，

    属性名 数据类型[约束条件]，

    ......

   [unique|fulltext|spatial] index }key[别名](属性名[ASC|DESC])

);

Create a regular index

#普通索引
create table score
(
	id int auto_increment primary key not null,
	name varchar(30) not null,
	math int not null,
	english int not null,
	chinese int not null,
	index(id)
);

show create table score;

Create a unique index

#唯一索引
create table t_address
(
	id int auto_increment primary key not null,
	name varchar(30),
	address varchar(200),
	unique index UQ_address(id asc)
);

show create table t_address

Create a full-text index

#全文索引
create table cards
(id int auto_increment primary key not null,
name varchar(30),
number int,
info varchar(50),
fulltext key ftk_number(number)
)ENGINE=MyISAM DEFAULT CHARSET=utf8;

MySql comes with the full-text index can only be used for the database engine MYISAM data sheet, if other data engine, the full-text index will not take effect. In addition, MySql comes with full-text indexing full-text search can only be conducted in English, Chinese is currently unable to perform full-text search. If you need to text data included Chinese, including full-text search, we need to use Sphinx (Sphinx) / Coreseek technology to deal with Chinese.

Currently, when using MySql comes with the full-text index, if the query string is too short you will not get the desired search results. MySql full-text indexing can find the default minimum word length is 4 characters. In addition, if the query string contains stop words, then the stop words will be ignored.

If possible, try to create tables and insert all the data and then create a full-text index, but do not directly create full-text index When you create a table, because the former is higher than the latter's full-text indexing efficiency.

Create a separate index

#单列索引
create table telephone
(
	id int auto_increment primary KEY not null,
	name varchar(30),
	tel varchar(30),
	index idx_tel(tel(20))
);

Create multi-column index

#多列索引
create table information
(
	id int primary key auto_increment not null,
	name varchar(30) not null,
	sex varchar(30) not null,
	birthday VARCHAR(30) not null,
	index idx_name_sex(name,sex)
);

Create a spatial index

 

#空间索引
create table list
(
	id int PRIMARY key auto_increment not null,
	goods geometry not null,
	spatial index spt(goods)
)engine=myisam;

Open data table to create an index 

语法：
   create [unique|fulltext|spatial] index index_name
   on table_name(属性[(length)][ASC|DESC]);

#在已有的表上创建索引
create index idx_id on t1(id)

 

Add index structure modification data table

语法：
  alter table table_name add[unique|fulltext|spatial] index index_name(属性名[(length)][ASC|DESC]);

#添加索引
alter table t1
add unique index idx_name(name(10))

 

Delete Index 

语法:
     drop index  index_name  on table_name


#删除索引
drop index idx_name on t1