Mysql: 利用强制索引去掉重数据

数据库版本：

[root@mysqltest ~]# mysql -u root -p123456

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 389805

Server version: 5.1.73-community MySQL Community Server (GPL)

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affiliates. Other names may be trademarks of their respective

owners.

Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.

mysql>

mysql> show databases;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| cacti              |

| centreon           |

| centreon_status    |

| centreon_storage   |

| mysql              |

| syslog             |

| test               |

+--------------------+

8 rows in set (0.01 sec)

1 .创建实验使用的a b表

mysql> use test;

Database changed

mysql> show tables;

Empty set (0.00 sec)

mysql> create table a (a1 char(10), a2 char(10), a3 char(10));

Query OK, 0 rows affected (0.08 sec)

mysql> insert into a values (‘1‘, ‘2‘, ‘3‘);

Query OK, 1 row affected (0.00 sec)

mysql> insert into a select * from a;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

。

。

。

。

mysql> insert into a select * from a;

Query OK, 4194304 rows affected (7.85 sec)

Records: 4194304  Duplicates: 0  Warnings: 0

mysql> insert into a select * from a;

Query OK, 8388608 rows affected (27.81 sec)

Records: 8388608  Duplicates: 0  Warnings: 0

2  创建b表：

mysql> create table b (b1 char (10), b2 char(10), b3 char(10));

Query OK, 0 rows affected (0.06 sec)

mysql> insert into b select * from a;

Query OK, 16777216 rows affected (1 min 6.18 sec)

Records: 16777216  Duplicates: 0  Warnings: 0

mysql>

mysql>

mysql> commit;

Query OK, 0 rows affected (0.00 sec)

mysql>

mysql>

mysql> select * from b limit 10;

+------+------+------+

| b1   | b2   | b3   |

+------+------+------+

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

+------+------+------+

10 rows in set (0.04 sec)

3  加入b表不同样的数据

mysql> insert into b values (‘4‘,‘5‘,‘6‘);

Query OK, 1 row affected (0.01 sec)

mysql> insert into b values (‘4‘,‘5‘,‘6‘);

Query OK, 1 row affected (0.00 sec)

mysql> insert into b values (‘4‘,‘5‘,‘6‘);

Query OK, 1 row affected (0.00 sec)

mysql> insert into b values (‘4‘,‘5‘,‘6‘);

Query OK, 1 row affected (0.00 sec)

mysql>

mysql> insert into b values (‘4‘,‘5‘,‘6‘);

Query OK, 1 row affected (0.00 sec)

mysql> commit

-> ;

Query OK, 0 rows affected (0.00 sec)

mysql>

mysql>

mysql>

4 查看a b表数据行数

mysql> select count(1) from b;

+----------+

| count(1) |

+----------+

| 16777224 |

+----------+

1 row in set (0.00 sec)

mysql> select count(1) from a;

+----------+

| count(1) |

+----------+

| 16777216 |

+----------+

1 row in set (0.00 sec)

5 创建c表

mysql> create table c (c1 char (10), c2 char(10), c3 char(10));

Query OK, 0 rows affected (0.31 sec)

6 创建临时temp表

mysql> create table temp select * from c where 1=2;

Query OK, 0 rows affected (0.06 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from temp;

Empty set (0.00 sec)

mysql> desc temp;

+-------+----------+------+-----+---------+-------+

| Field | Type     | Null | Key | Default | Extra |

+-------+----------+------+-----+---------+-------+

| c1    | char(10) | YES  |     | NULL    |       |

| c2    | char(10) | YES  |     | NULL    |       |

| c3    | char(10) | YES  |     | NULL    |       |

+-------+----------+------+-----+---------+-------+

3 rows in set (0.02 sec)

7 为b表创建索引

mysql> create index ind_b_b1 on b(b1);

Query OK, 16777224 rows affected (2 min 9.14 sec)

Records: 16777224  Duplicates: 0  Warnings: 0

mysql> desc b;

+-------+----------+------+-----+---------+-------+

| Field | Type     | Null | Key | Default | Extra |

+-------+----------+------+-----+---------+-------+

| b1    | char(10) | YES  | MUL | NULL    |       |

| b2    | char(10) | YES  |     | NULL    |       |

| b3    | char(10) | YES  |     | NULL    |       |

+-------+----------+------+-----+---------+-------+

3 rows in set (0.02 sec)

8 把a b表数据插入temp表中

mysql> insert into temp select * from a;

Query OK, 16777216 rows affected (29.84 sec)

Records: 16777216  Duplicates: 0  Warnings: 0

mysql> insert into temp select * from b;

Query OK, 16777224 rows affected (59.79 sec)

Records: 16777224  Duplicates: 0  Warnings: 0

mysql>

mysql>

mysql> commit;

Query OK, 0 rows affected (0.00 sec)

mysql> select count(1) from temp;

+----------+

| count(1) |

+----------+

| 33554440 |

+----------+

1 row in set (0.00 sec)

9 创建联合索引      强制索引去掉重复数据

mysql> create index ind_temp_c123 on temp(c1, c2, c3);

Query OK, 33554440 rows affected (6 min 57.80 sec)

Records: 33554440  Duplicates: 0  Warnings: 0

mysql>

mysql>

mysql> explain select c1, c2, max(c3) from temp force index (ind_temp_c123) group by c1, c2;

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

| id | select_type | table | type  | possible_keys | key           | key_len | ref  | rows | Extra                    |

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

|  1 | SIMPLE      | temp  | range | NULL          | ind_temp_c123 | 22      | NULL |    3 | Using index for group-by |

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

1 row in set (0.00 sec)

mysql> select count(*) from temp;

+----------+

| count(*) |

+----------+

| 33554440 |

+----------+

1 row in set (0.00 sec)

mysql> explain select c1, c2, c3 from temp force index (ind_temp_c123) group by c1, c2;

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

| id | select_type | table | type  | possible_keys | key           | key_len | ref  | rows | Extra                    |

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

|  1 | SIMPLE      | temp  | range | NULL          | ind_temp_c123 | 22      | NULL |    3 | Using index for group-by |

+----+-------------+-------+-------+---------------+---------------+---------+------+------+--------------------------+

1 row in set (0.00 sec)

mysql> insert into c select c1, c2, max(c3) from temp force index (ind_temp_c123) group by c1, c2;

Query OK, 2 rows affected (0.03 sec)

Records: 2  Duplicates: 0  Warnings: 0

10 去重复后c表的数据

mysql> select * from c;

+------+------+------+

| c1   | c2   | c3   |

+------+------+------+

| 1    | 2    | 3    |

| 4    | 5    | 6    |

+------+------+------+

2 rows in set (0.00 sec)

mysql>

mysql>

mysql> select * from temp order by c1 desc limit 10;

+------+------+------+

| c1   | c2   | c3   |

+------+------+------+

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 4    | 5    | 6    |

| 1    | 2    | 3    |

| 1    | 2    | 3    |

+------+------+------+

10 rows in set (0.00 sec)

mysql> Ctrl-C -- exit!

Aborted

11 删除表 temp

mysql> drop table temp;

Query OK, 0 rows affected (1.59 sec)

mysql> drop table a;

Query OK, 0 rows affected (0.55 sec)

mysql> drop table b;

Query OK, 0 rows affected (0.73 sec)

mysql> show tables;

+----------------+

| Tables_in_test |

+----------------+

| c              |

+----------------+

1 row in set (0.00 sec)

mysql>