Question

我正在为邮件收件箱开发一个大表像

这样的查询

解释SELECT * FROM messages where（receptor='x1@yahoo.com'和sender='x2@yahoo.com'）或（sender ='x1@yahoo.com'和receptor='x2@yahoo.com '）由id desc LIMIT 10命令;

非常慢并导致挂起服务器请让我知道如何索引此表或更改查询以避免此问题感谢

表格结构

mysql> DESCRIBE messages;                  
+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| id       | bigint(20)   | NO   | PRI | NULL    | auto_increment | 
| sender   | varchar(65)  | NO   | MUL | NULL    |                | 
| is_sdel  | tinyint(1)   | NO   |     | NULL    |                | 
| receptor | varchar(65)  | NO   | MUL | NULL    |                | 
| is_rdel  | tinyint(1)   | NO   |     | NULL    |                | 
| dtime    | varchar(100) | NO   | MUL | NULL    |                | 
| title    | longtext     | NO   |     | NULL    |                | 
| com      | longtext     | NO   |     | NULL    |                | 
| ipu      | varchar(15)  | NO   |     | NULL    |                | 
| flage    | tinyint(2)   | NO   |     | NULL    |                | 
| view     | tinyint(2)   | NO   | MUL | NULL    |                | 
+----------+--------------+------+-----+---------+----------------+
11 rows in set (0.00 sec)

解释命令结果

 explain SELECT * FROM messages where (receptor='x1@yahoo.com' and sender='x2@yahoo.com') or (sender='x1@yahoo.com' and receptor='x2@yahoo.com') order by id desc LIMIT 10;
+----+-------------+----------+-------+--------------------------------------------------------------------------------+--------------------+---------+------+------+-----------------------------+
| id | select_type | table    | type  | possible_keys                                                                  | key                | key_len | ref  | rows | Extra                       |
+----+-------------+----------+-------+--------------------------------------------------------------------------------+--------------------+---------+------+------+-----------------------------+
|  1 | SIMPLE      | messages | range | sender,receptor,receptor-id,receptor-view,sender-receptor-id,sender-is_sdel-id | sender-receptor-id | 134     | NULL |    4 | Using where; Using filesort | 
+----+-------------+----------+-------+--------------------------------------------------------------------------------+--------------------+---------+------+------+-----------------------------+
1 row in set (0.01 sec)

Answer 1

在WHERE列（受体，发件人）

上创建索引

CREATE UNIQUE INDEX sender_index
ON messages (sender)

CREATE UNIQUE INDEX recever_index
ON messages (recever)

Answer 2

从评论中提交我的回答：

SELECT * FROM (
  SELECT * FROM messages
  WHERE (receptor='x1@yahoo.com' and sender='x2@yahoo.com')
    or (sender='x1@yahoo.com' and receptor='x2@yahoo.com')
) x
order by id desc
LIMIT 10;

您遇到的问题是排序非常大的桌子。此解决方案强制MySQL首先过滤掉内部查询中的消息，然后仅在外部查询中对这些消息进行排序。

如何索引表字段

表格结构

2 个答案: