蝙蝠岛资源网 Design By www.hbtsch.com
很多开发人员在使用MySQL时经常会在部分列上进行函数计算等,导致无法走索引,在数据量大的时候,查询效率低下。针对此种情况本文从MySQL5.7 及MySQL8.0中分别进行不同方式的优化。
1、 MySQL5.7
MySQL5.7版本中不支持函数索引,因此 遇到函数索引的时候需要进行修改,否则即使查询的字段上有索引,执行时也无法使用索引而进行全表扫描,数据量大的表查询时间会比较长。具体案例如下:
1.1 创建测试表及数据
mysql> use testdb; Database changed mysql> create table tb_function(id int primary key auto_increment,name varchar(100),create_time datetime); Query OK, 0 rows affected (0.01 sec) mysql> insert into tb_function(name,creatE_time) values('anniuadaOAIFAPUHIA','2020-07-01 12:00:00'); Query OK, 1 row affected (0.02 sec) mysql> insert into tb_function(name,creatE_time) values('CWQSsar3qcssg','2020-07-01 15:00:00'); Query OK, 1 row affected (0.01 sec) mysql> insert into tb_function(name,creatE_time) values('vxfqrt2adafz','2020-07-01 21:30:00'); Query OK, 1 row affected (0.01 sec) mysql> insert into tb_function(name,creatE_time) values('etxzwrwbdhegqgaheqhag','2020-07-02 01:30:00'); Query OK, 1 row affected (0.01 sec) mysql> insert into tb_function(name,creatE_time) values('awrs433fsgvsfwtwg','2020-07-02 03:30:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('awrs433fsgvsfwtwg','2020-07-02 07:32:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('awrs433fsgvsfwtwg','2020-07-02 10:32:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('tuilklmdadq','2020-07-02 15:32:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('wesv2wqdshehq','2020-07-02 20:32:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('89yoijnlkwr1','2020-07-03 02:56:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into tb_function(name,creatE_time) values('olj;nsaaq','2020-07-03 08:41:00'); Query OK, 1 row affected (0.01 sec) mysql> insert into tb_function(name,creatE_time) values('ygo;jkdsaq','2020-07-03 16:20:00'); Query OK, 1 row affected (0.01 sec) mysql> select * from tb_function; +----+-----------------------+---------------------+ | id | name | create_time | +----+-----------------------+---------------------+ | 1 | anniuadaOAIFAPUHIA | 2020-07-01 12:00:00 | | 2 | CWQSsar3qcssg | 2020-07-01 15:00:00 | | 3 | vxfqrt2adafz | 2020-07-01 21:30:00 | | 4 | etxzwrwbdhegqgaheqhag | 2020-07-02 01:30:00 | | 5 | awrs433fsgvsfwtwg | 2020-07-02 03:30:00 | | 6 | awrs433fsgvsfwtwg | 2020-07-02 07:32:00 | | 7 | awrs433fsgvsfwtwg | 2020-07-02 10:32:00 | | 8 | tuilklmdadq | 2020-07-02 15:32:00 | | 9 | wesv2wqdshehq | 2020-07-02 20:32:00 | | 10 | 89yoijnlkwr1 | 2020-07-03 02:56:00 | | 11 | olj;nsaaq | 2020-07-03 08:41:00 | | 12 | ygo;jkdsaq | 2020-07-03 16:20:00 | +----+-----------------------+---------------------+ 12 rows in set (0.00 sec)
1.2 创建索引
在create_time字段上创建索引
mysql> alter table tb_function add key idx_create_time(create_time); Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0
1.3 按时间查询
查询创建时间是2020-07-01那天的所有记录
mysql> select * from tb_function where date(create_time)='2020-07-01'; +----+--------------------+---------------------+ | id | name | create_time | +----+--------------------+---------------------+ | 1 | anniuadaOAIFAPUHIA | 2020-07-01 12:00:00 | | 2 | CWQSsar3qcssg | 2020-07-01 15:00:00 | | 3 | vxfqrt2adafz | 2020-07-01 21:30:00 | +----+--------------------+---------------------+ 3 rows in set (0.00 sec)
执行计划如下:
mysql> explain select * from tb_function where date(create_time)='2020-07-01'; +----+-------------+-------------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | tb_function | NULL | ALL | NULL | NULL | NULL | NULL | 12 | 100.00 | Using where | +----+-------------+-------------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
执行计划中可以看出是进行了全面扫描
1.4 优化
因MySQL5.7不支持函数索引,所以需要修改SQL写法来实现走索引(或者使用虚拟列的方式),上述SQL可以修改为
mysql> select * from tb_function where create_time>='2020-07-01' and create_time<date_add('2020-07-01',INTERVAL 1 day); +----+--------------------+---------------------+ | id | name | create_time | +----+--------------------+---------------------+ | 1 | anniuadaOAIFAPUHIA | 2020-07-01 12:00:00 | | 2 | CWQSsar3qcssg | 2020-07-01 15:00:00 | | 3 | vxfqrt2adafz | 2020-07-01 21:30:00 | +----+--------------------+---------------------+ 3 rows in set (0.00 sec)
执行计划如下:
mysql> explain select * from tb_function where create_time>='2020-07-01' and create_time<date_add('2020-07-01',INTERVAL 1 day); +----+-------------+-------------+------------+-------+-----------------+-----------------+---------+------+------+----------+-----------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------------+------------+-------+-----------------+-----------------+---------+------+------+----------+-----------------------+ | 1 | SIMPLE | tb_function | NULL | range | idx_create_time | idx_create_time | 6 | NULL | 3 | 100.00 | Using index condition | +----+-------------+-------------+------------+-------+-----------------+-----------------+---------+------+------+----------+-----------------------+ 1 row in set, 1 warning (0.00 sec)
可见,修改后,使用了索引。
2、MySQL8.0
MySQL8.0的索引特性增加了函数索引。其实MySQL5.7中推出了虚拟列的功能,而MySQL8.0的函数索引也是依据虚拟列来实现的。将上述的案例在MySQL8.0中实现情况如下文所述。
2.1 创建函数索引
在将上述的表及数据在MySQL8.0的实例上创建,然后创建create_time的函数索引,SQL如下
mysql> alter table tb_function add key idx_create_time((date(create_time))); -- 注意里面字段的括号 Query OK, 0 rows affected (0.10 sec) Records: 0 Duplicates: 0 Warnings: 0
2.2 按时间查询
mysql> select * from tb_function where date(create_time)='2020-07-01'; +----+--------------------+---------------------+ | id | name | create_time | +----+--------------------+---------------------+ | 1 | anniuadaOAIFAPUHIA | 2020-07-01 12:00:00 | | 2 | CWQSsar3qcssg | 2020-07-01 15:00:00 | | 3 | vxfqrt2adafz | 2020-07-01 21:30:00 | +----+--------------------+---------------------+ 3 rows in set (0.00 sec)
执行计划如下
mysql> explain select * from tb_function where date(create_time)='2020-07-01'; +----+-------------+-------------+------------+------+-----------------+-----------------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------------+------------+------+-----------------+-----------------+---------+-------+------+----------+-------+ | 1 | SIMPLE | tb_function | NULL | ref | idx_create_time | idx_create_time | 4 | const | 3 | 100.00 | NULL | +----+-------------+-------------+------------+------+-----------------+-----------------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.00 sec)
可见,在MySQL8.0 创建对应的函数索引后,不改变SQL写法的前提下,查询的列上进行对应的函数计算后也可以走索引。
关于MySQL函数索引的优化及MySQL8.0函数索引还可以有更多的场景进行测试,建议大家多动手试试,提高SQL改写及优化的能力。
以上就是MySQL 函数索引的优化方案的详细内容,更多关于MySQL 函数索引及优化方案的资料请关注其它相关文章!
蝙蝠岛资源网 Design By www.hbtsch.com
广告合作:本站广告合作请联系QQ:858582 申请时备注:广告合作(否则不回)
免责声明:本站文章均来自网站采集或用户投稿,网站不提供任何软件下载或自行开发的软件! 如有用户或公司发现本站内容信息存在侵权行为,请邮件告知! 858582#qq.com
免责声明:本站文章均来自网站采集或用户投稿,网站不提供任何软件下载或自行开发的软件! 如有用户或公司发现本站内容信息存在侵权行为,请邮件告知! 858582#qq.com
蝙蝠岛资源网 Design By www.hbtsch.com
暂无MySQL 函数索引的优化方案的评论...
更新日志
2024年12月23日
2024年12月23日
- 小骆驼-《草原狼2(蓝光CD)》[原抓WAV+CUE]
- 群星《欢迎来到我身边 电影原声专辑》[320K/MP3][105.02MB]
- 群星《欢迎来到我身边 电影原声专辑》[FLAC/分轨][480.9MB]
- 雷婷《梦里蓝天HQⅡ》 2023头版限量编号低速原抓[WAV+CUE][463M]
- 群星《2024好听新歌42》AI调整音效【WAV分轨】
- 王思雨-《思念陪着鸿雁飞》WAV
- 王思雨《喜马拉雅HQ》头版限量编号[WAV+CUE]
- 李健《无时无刻》[WAV+CUE][590M]
- 陈奕迅《酝酿》[WAV分轨][502M]
- 卓依婷《化蝶》2CD[WAV+CUE][1.1G]
- 群星《吉他王(黑胶CD)》[WAV+CUE]
- 齐秦《穿乐(穿越)》[WAV+CUE]
- 发烧珍品《数位CD音响测试-动向效果(九)》【WAV+CUE】
- 邝美云《邝美云精装歌集》[DSF][1.6G]
- 吕方《爱一回伤一回》[WAV+CUE][454M]