跟一个朋友，不错公司的主管交流时，对于mysql中条件查询和排序时 与索引的关系
mysql> explain select * from article where title='希望光伏企业挺过2个月' o
rder by id desc\\\\\\\\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: article
type: index
possible_keys: NULL
key: PRIMARY
key_len: 4
ref: NULL
rows: 567
Extra: Using where
1 row in set (0.00 sec)
mysql> select * from article where title='希望光伏企业挺过2个月';
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
| id | category_id | user_id | app_id | title | subtitle |
professor | money | cooperation | project | address | discription
| source | r
ecommend | status | ctime | mtime |
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
| 10 | 2 | 4 | 0 | 希望光伏企业挺过2个月 | |
| 0 | | | | 希望企业挺过两个月。 | |
1 | 0 | 1371524848 | 1371525226 |
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
1 row in set (0.00 sec)
mysql> explain select * from article where title='希望光伏企业挺过2个月';
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | ro
ws | Extra |
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
| 1 | SIMPLE | article | ALL | NULL | NULL | NULL | NULL | 5
67 | Using where |
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
1 row in set (0.00 sec)
大部门的开发人员会认为第一种查询时，不会用到索引
