MySQL 函数索引的优化方案

MySQL 函数索引的优化方案

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。

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原文链接:https://www.cnblogs.com/gjc592/p/13233377.html