MySQL：索引的类型及相关优化

一、索引类型

• 单列索引
  
  • 普通索引index :加速查找
• 唯一索引
  
  • 主键索引：primary key ：加速查找+约束（不为空且唯一）
  • 唯一索引：unique：加速查找+约束 （唯一）
• 联合索引
  
  • primary key(id,name):联合主键索引
  • unique(id,name):联合唯一索引
  • index(id,name):联合普通索引
• 全文索引fulltext :用于搜索很长一篇文章的时候，效果最好。
• 空间索引spatial :了解就好，几乎不用

二、DDL

MySQL创建索引的语法：

CREATE [UNIQUE | FULLTEXT | SPATIAL] INDEX index_name
    [index_type]
    ON tbl_name (key_part,...)
    [index_option]
    [algorithm_option | lock_option] ...

其中各个部分的解释：

• key_part:

  col_name [(length)] [ASC | DESC]

• index_option:

  KEY_BLOCK_SIZE [=] value
  | index_type
  | WITH PARSER parser_name
  | COMMENT 'string'

  • Table 13.2 InnoDB Storage Engine Index Characteristics

    Index Class	Index Type	Stores NULL VALUES	Permits Multiple NULL Values	IS NULL Scan Type	IS NOT NULL Scan Type
    Primary key	BTREE	No	No	N/A	N/A
    Unique	BTREE	Yes	Yes	Index	Index
    Key	BTREE	Yes	Yes	Index	Index
    FULLTEXT	N/A	Yes	Yes	Table	Table
    SPATIAL	N/A	No	No	N/A	N/A

  • Table 13.3 MyISAM Storage Engine Index Characteristics

    Index Class	Index Type	Stores NULL VALUES	Permits Multiple NULL Values	IS NULL Scan Type	IS NOT NULL Scan Type
    Primary key	BTREE	No	No	N/A	N/A
    Unique	BTREE	Yes	Yes	Index	Index
    Key	BTREE	Yes	Yes	Index	Index
    FULLTEXT	N/A	Yes	Yes	Table	Table
    SPATIAL	N/A	No	No	N/A	N/A

  • Table 13.4 MEMORY Storage Engine Index Characteristics

    Index Class	Index Type	Stores NULL VALUES	Permits Multiple NULL Values	IS NULL Scan Type	IS NOT NULL Scan Type
    Primary key	BTREE	No	No	N/A	N/A
    Unique	BTREE	Yes	Yes	Index	Index
    Key	BTREE	Yes	Yes	Index	Index
    Primary key	HASH	No	No	N/A	N/A
    Unique	HASH	Yes	Yes	Index	Index
    Key	HASH	Yes	Yes	Index	Index

• index_type:

  USING {BTREE | HASH}

  Storage Engine	Permissible Index Types
  InnoDB	BTREE
  MyISAM	BTREE
  MEMORY/HEAP	HASH, BTREE

• algorithm_option:

  ALGORITHM [=] {DEFAULT | INPLACE | COPY}

• lock_option:

  LOCK [=] {DEFAULT | NONE | SHARED | EXCLUSIVE}

具体可参考MySQL 5.7 Reference Manual CREATE INDEX Syntax

参考资料

MySQL官方文档：SQL语句语法