这里的分表逻辑是根据t_group表的user_name组的个数来分的。 因为这种情况单独user_name字段上的索引就属于烂索引。起不了啥名明显的效果。 1、试验PROCEDURE. DELIMITER $$ DROP PROCEDURE `t_girl`
这里的分表逻辑是根据t_group表的user_name组的个数来分的。因为这种情况单独user_name字段上的索引就属于烂索引。起不了啥名明显的效果。1、试验PROCEDURE.DELIMITER $$DROP PROCEDURE `t_girl`.`sp_split_table`$$CREATE PROCEDURE `t_girl`.`sp_split_table`()BEGIN declare done int default 0; declare v_user_name varchar(20) default ''; declare v_table_name varchar(64) default ''; -- Get all users' name. declare cur1 cursor for select user_name from t_group group by user_name; -- Deal with error or warnings. declare continue handler for 1329 set done = 1; -- Open cursor. open cur1; while done <> 1 do fetch cur1 into v_user_name; if not done then -- Get table name. set v_table_name = concat('t_group_',v_user_name); -- Create new extra table. set @stmt = concat('create table ',v_table_name,' like t_group'); prepare s1 from @stmt; execute s1; drop prepare s1; -- Load data into it. set @stmt = concat('insert into ',v_table_name,' select * from t_group where user_name = ''',v_user_name,''''); prepare s1 from @stmt; execute s1; drop prepare s1; end if; end while; -- Close cursor. close cur1; -- Free variable from memory. set @stmt = NULL;END$$DELIMITER ;2、试验表。我们用一个有一千万条记录的表来做测试。mysql> select count(*) from t_group;+----------+| count(*) |+----------+| 10388608 | +----------+1 row in set (0.00 sec)表结构。mysql> desc t_group;+-------------+------------------+------+-----+-------------------+----------------+| Field | Type | Null | Key | Default | Extra |+-------------+------------------+------+-----+-------------------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment | | money | decimal(10,2) | NO | | | | | user_name | varchar(20) | NO | MUL | | | | create_time | timestamp | NO | | CURRENT_TIMESTAMP | | +-------------+------------------+------+-----+-------------------+----------------+4 rows in set (0.00 sec)索引情况。mysql> show index from t_group;+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+| t_group | 0 | PRIMARY | 1 | id | A | 10388608 | NULL | NULL | | BTREE | | | t_group | 1 | idx_user_name | 1 | user_name | A | 8 | NULL | NULL | | BTREE | | | t_group | 1 | idx_combination1 | 1 | user_name | A | 8 | NULL | NULL | | BTREE | | | t_group | 1 | idx_combination1 | 2 | money | A | 3776 | NULL | NULL | | BTREE | | +---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+4 rows in set (0.00 sec)PS:idx_combination1 这个索引是必须的，因为要对user_name来GROUP BY。此时属于松散索引扫描！当然完了后你可以干掉她。idx_user_name 这个索引是为了加快单独执行constant这种类型的查询。我们要根据用户名来分表。mysql> select user_name from t_group where 1 group by user_name;+-----------+| user_name |+-----------+| david | | leo | | livia | | lucy | | sarah | | simon | | sony | | sunny | +-----------+8 rows in set (0.00 sec)所以结果表应该是这样的。mysql> show tables like 't_group_%';+------------------------------+| Tables_in_t_girl (t_group_%) |+------------------------------+| t_group_david | | t_group_leo | | t_group_livia | | t_group_lucy | | t_group_sarah | | t_group_simon | | t_group_sony | | t_group_sunny | +------------------------------+8 rows in set (0.00 sec)3、对比结果。mysql> select count(*) from t_group where user_name = 'david';+----------+| count(*) |+----------+| 1298576 | +----------+1 row in set (1.71 sec)执行了将近2秒。mysql> select count(*) from t_group_david;+----------+| count(*) |+----------+| 1298576 | +----------+1 row in set (0.00 sec)几乎是瞬间的。mysql> select count(*) from t_group where user_name <> 'david';+----------+| count(*) |+----------+| 9090032 | +----------+1 row in set (9.26 sec)执行了将近10秒，可以想象，这个是实际的项目中是不能忍受的。mysql> select (select count(*) from t_group) - (select count(*) from t_group_david) as total;+---------+| total |+---------+| 9090032 | +---------+1 row in set (0.00 sec)几乎是瞬间的。我们来看看聚集函数。对于原表的操作。mysql> select min(money),max(money) from t_group where user_name = 'david';+------------+------------+| min(money) | max(money) |+------------+------------+| -6.41 | 500.59 | +------------+------------+1 row in set (0.00 sec)最小，最大值都是FULL INDEX SCAN。所以是瞬间的。mysql> select sum(money),avg(money) from t_group where user_name = 'david';+--------------+------------+| sum(money) | avg(money) |+--------------+------------+| 319992383.84 | 246.417910 | +--------------+------------+1 row in set (2.15 sec)其他聚集函数的结果就不是FULL INDEX SCAN了。耗时2.15秒。对于小表的操作。mysql> select min(money),max(money) from t_group_david;+------------+------------+| min(money) | max(money) |+------------+------------+| -6.41 | 500.59 | +------------+------------+1 row in set (1.50 sec)最大最小值完全是FULL TABLE SCAN,耗时1.50秒，不划算。以此看来。mysql> select sum(money),avg(money) from t_group_david;+--------------+------------+| sum(money) | avg(money) |+--------------+------------+| 319992383.84 | 246.417910 | +--------------+------------+1 row in set (1.68 sec)取得这两个结果也是花了快2秒，快了一点。我们来看看这个小表的结构。mysql> desc t_group_david;+-------------+------------------+------+-----+-------------------+----------------+| Field | Type | Null | Key | Default | Extra |+-------------+------------------+------+-----+-------------------+----------------+| id | int(10) unsigned | NO | PRI | NULL | auto_increment | | money | decimal(10,2) | NO | | | | | user_name | varchar(20) | NO | MUL | | | | create_time | timestamp | NO | | CURRENT_TIMESTAMP | | +-------------+------------------+------+-----+-------------------+----------------+4 rows in set (0.00 sec)明显的user_name属性是多余的。那么就干掉它。mysql> alter table t_group_david drop user_name;Query OK, 1298576 rows affected (7.58 sec)Records: 1298576 Duplicates: 0 Warnings: 0现在来重新对小表运行查询mysql> select min(money),max(money) from t_group_david;+------------+------------+| min(money) | max(money) |+------------+------------+| -6.41 | 500.59 | +------------+------------+1 row in set (0.00 sec)此时是瞬间的。mysql> select sum(money),avg(money) from t_group_david;+--------------+------------+| sum(money) | avg(money) |+--------------+------------+| 319992383.84 | 246.417910 | +--------------+------------+1 row in set (0.94 sec)这次算是控制在一秒以内了。mysql> Aborted小总结一下：分出的小表的属性尽量越少越好。大胆的去干吧。
