1.计算数据表中一共有多少记录sql语句 
> select count(*) from openes; 
+----------+ 
| count(*) | 
+----------+ 
|      136 | 
+----------+ 
1 row in set (0.00 sec) 
 
2.查询字段类型为datetime的SQL语句： 
 
mysql> select * from biders where author_id =2253 and created_at between   '2012-3-19   00:00:00 '   and   '2012-3-19   23:59:59 
'; 
+----+-----------+---------------------+---------------------+---------------------+ 
| id | author_id | created_at          | updated_at          | num_of_target_files | 
+----+-----------+---------------------+---------------------+---------------------+ 
|  10 |      2353 | 2012-3-19 15:21:08 | 2012-3-19 15:21:08 |                NULL | 
+----+-----------+---------------------+---------------------+---------------------+ 
1 row in set (0.00 sec)