我們的項目中有好多不等於的情況。今天寫這篇文章簡單的分析一下怎麼個優化法。
這裡的分表邏輯是根據t_group表的user_name組的個數來分的。
因為這種情況單獨user_name字段上的索引就屬於爛索引。起不了啥名明顯的效果。
1、試驗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、試驗表。
我們用一個有一千萬條記錄的表來做測試。
mysql> select count(*) from t_group;
+----------+
| count(*) |
+----------+
| 10388608 |
+----------+
1 row in set (0.00 sec)
表結構。
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)
索引情況。
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 這個索引是必須的，因為要對user_name來GROUP BY。此時屬於松散索引掃描！當然完了後你可以干掉她。
idx_user_name 這個索引是為了加快單獨執行constant這種類型的查詢。
我們要根據用戶名來分表。
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)
所以結果表應該是這樣的。
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 &n
