MYSQL中GROUP BY不包含所有的非聚合字段时的注意事项

select count(1),task_type,status from action where biz_date='20141014' group by status


select count(1),task_type from action where biz_date='20141014' group by status


		

mysql> select * from test;


+----+-------+------+-------+
| id | name  | age  | class |
+----+-------+------+-------+
|  1 | qiu   |   22 |     1 | 
|  2 | liu   |   42 |     1 | 
|  4 | zheng |   20 |     2 | 
|  3 | qian  |   20 |     2 | 
|  0 | wang  |   11 |     3 | 
|  6 | li    |   33 |     3 | 
+----+-------+------+-------+
6 rows in set (0.00 sec)

		

mysql> select id,name,max(age),class from test group by class;

+----+-------+----------+-------+
| id | name  | max(age) | class |
+----+-------+----------+-------+
|  1 | qiu   |       42 |     1 | 
|  4 | zheng |       20 |     2 | 
|  0 | wang  |       33 |     3 | 
+----+-------+----------+-------+
3 rows in set (0.00 sec)

		

select A.id, B.desc, B.XXX, B.YYY SUM(A.AMT) 
    FROM A
    join b on a.id=b.id
    where a.id=? and b.xxx=?
    group a.id