我回去查了一下关于mysql group by 奇怪的现像，
??? 可以通过修改sql_mode 的方法改变这种奇怪的现像。
??? 例如下：

mysql> SELECT job,sal,deptno
??? -> FROM emp
??? -> GROUP by deptno;
+----------+---------+--------+
| job????? | sal???? | deptno |
+----------+---------+--------+
| MANAGER? | 2450.00 |???? 10 |
| CLERK??? |? 800.00 |???? 20 |
| SALESMAN | 1600.00 |???? 30 |
+----------+---------+--------+
3 rows in set (0.04 sec)

mysql> set sql_mode = "STRICT_TRANS_TABLES,ONLY_FULL_GROUP_BY";
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT job,sal,deptno
??? -> FROM emp
??? -> GROUP by deptno;
ERROR 1055 (42000): 'tao.emp.JOB' isn't in GROUP BY
mysql> SELECT count(job),count(sal),deptno
??? -> FROM emp
??? -> GROUP BY deptno;
+------------+------------+--------+
| count(job) | count(sal) | deptno |
+------------+------------+--------+
|????????? 3 |????????? 3 |???? 10 |
|????????? 5 |????????? 5 |???? 20 |
|????????? 6 |????????? 6 |???? 30 |
+------------+------------+--------+
3 rows in set (0.00 sec)


//-------------------------------------------------
//以上修改sql_mode 只在当前会话中生效.
//如果需要长期有效请修改 my.ini 文件中

#sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
sql_mode = "STRICT_TRANS_TABLES,ONLY_FULL_GROUP_BY"