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任务描写叙述：

如果一高频查询例如以下

SELECT * FROM user WHERE area=‘amoy‘ AND sex=0 ORDER BY last_login DESC limit 30;

怎样建立索引？描写叙述考虑的过程

user表例如以下：

初始化100W条数据，当中。area要通过IP查询生成，sex为 0,1 随机

CREATE TABLE user (

id int(10) NOT NULL AUTOINCREMENT COMMENT ‘自增编号‘,

) ENGINE=InnoDB AUTOINCREMENT=892013 DEFAULT CHARSET=latin1

终于我的索引

(last_login,area)

数据例如以下：http://pan.baidu.com/s/1eQy0eQI

測试结果：http://pan.baidu.com/s/1jGn2AcY

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索引原则：

1.where和order by等的字段建立索引

2.使用唯一索引：对于last_login,area等字段反复的次数比較少，能够使用索引；而sex无非就两个值：性别1。男；2。不值得索引

3.多列索引：不要为每个列单独建立索引。这样并不能将mysql索引的效率最大化。使用“索引合并策略”

4.选择合理的索引列顺序：索引列的顺序意味着索引首先依照最左列进行排序。然后是第二列，以此类推。如(lastlogin,area)会先依照 lastlogin 进行排序。然后才是area。

5.将选择性最高的索引放到前面。也就是会所依照这个条件搜索到的数据最少，选择性就越高。比方选择性：last_login> area> sex。

6.索引不是越多越好。适合的索引能够提高查询效率。可是会减少写入效率。依据项目保持两者的平衡性最好了。

总结上面，首先sex不适合建立索引，有没有索引对于效率的提升意义不大，其次索引会依照最左列进行排序，因此将last_login放到最前面

測试过程：

user表

没有不论什么索引的查询相关日志：

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.57s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.56s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.55s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.59s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.55s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.55s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.57s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.58s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.57s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.57s

共花费时间：5.66s

建立索引area:

ALTER TABLE user ADD INDEX index_area (area)
;

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.06s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.10s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.11s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.20s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.07s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

共花费时间：0.66s

可见。建立area以后对性能的影响是巨大的(5.66/0.66 约为8.5758倍)

删除索引：ALTER TABLE user DROP INDEX index_area;

删除area索引发现时间又变成了0.57s

建立lastlogin索引：

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.03s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.09s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.51s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.07s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY last_login DESC limit 30; 0.06s

共花费时间：0.87s

相同可以提升性能（5.66/0.87 约为6.5057倍）

建立sex索引：

ALTER TABLE user ADD INDEX index_sex (sex)
;

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.89s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.88s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.86s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.88s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.87s

共花费时间：8.73s

相同可以提升性能（5.66s/8.73 约为0.6483倍）效率反而减少了？？求解？

建立这个sex索引还不如不建。

删除索引：

ALTER TABLE user DROP INDEX index_sex;

发现时间又变成了0.57s左右，

建立两个单独的索引：

ALTER TABLE user

ADD INDEX index_area (area)
,

ADD INDEX index_last_login (last_login)
;

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.09s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.33s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.21s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.28s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.03s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.67s

发现建立两个单独的索引还不如仅仅建立一个索引

删除索引：

发现时间又变成了0.57s左右。

建立一个的联合索引：

ALTER TABLE user

ADD INDEX index_last_login_area (last_login,area)
,

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.00s

额。第二条数据这是怎么了，我測试了5次都在这附近晃悠哈！

这尼玛。找对索引啦。就该这么建立，查询不出来须要的时间啦！预计就是我们须要的索引啦！

！

！！

删除索引：

发现时间又变成了0.57s左右，

建立一个的联合索引：

ALTER TABLE user

ADD INDEX index_sex_last_login_area (sex,last_login,area)

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.18s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.17s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.81s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.01s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.03s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

sex怎么总是你在拖后腿啊！

把你调整到索引的最后一个吧。

删除索引：

发现时间又变成了0.57s左右，

建立一个的联合索引：

ALTER TABLE user

ADD INDEX index_last_login_area_sex (area,last_login,sex)

SELECT * FROM user WHERE area=‘美国ATT用户‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.03s

SELECT * FROM user WHERE area=‘泰国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.07s

SELECT * FROM user WHERE area=‘台湾省台湾大宽频‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.50s

SELECT * FROM user WHERE area=‘美国弗吉尼亚州‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘德国奔驰汽车‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.05s

SELECT * FROM user WHERE area=‘台湾省中华电信‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.06s

SELECT * FROM user WHERE area=‘韩国‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘拉美地区‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.02s

SELECT * FROM user WHERE area=‘美国纽约(Prudential)‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.04s

SELECT * FROM user WHERE area=‘印度尼西亚‘ AND sex=0 ORDER BY lastlogin DESC limit 30; 0.06s

综上所述：1.建立索引不一定可以加快查询效率如sex这样的给反复次数特别多的列添加索引如sex这样的会减少查询效率，详细的原因有待查找

2.给反复次数比較少的列添加索引还是可以大幅度提高效率

3.给where和orderby之后的字段加入索引才会加快查询效率

4.为每个列单独建立索引，不能将索引的效率最大化，应该使用索引合并策略，即依据查询条件。建立联合索引

5.联合索引的顺序问题：将选择性高的索引放到前面

6.依据资料建立索引意味着索引依照最左列进行排序，然后事第二列。以此类推。如（lastlogin ,area）就会依照lastlogin进行排序，然后才是area

7.依据这次的这个查询条件来说最好的索引是：ALTER TABLE userADD INDEX index_last_login_area (last_login,area)。

在公司能有个机会。查看资料和实践索引真的非常不错哈！

推荐书籍：高性能mysql（第三版）

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