要将如下的数据：
+--------+--------+
| deptno | ename |
+--------+--------+
| 30 | ALLEN |
| 30 | WARD |
| 30 | MARTIN |
| 30 | BLAKE |
| 10 | CLARK |
| 10 | KING |
| 30 | TURNER |
| 30 | JAMES |
| 10 | MILLER |
+--------+--------+
转换为下列内容：
deptno emps
-------- --------------------------------
10 CLARK,KING,MILLER
30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
解决方案：
select deptno,
group_concat(ename order by empno separator ',')
from emp
group by deptno;
+--------+--------------------------------------+
| deptno | emps |
+--------+--------------------------------------+
| 10 | CLARK,KING,MILLER |
| 30 | ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES |
+--------+--------------------------------------+