Question

想象一下这张表t1，

+----------+-------+--------+
| group_id |  name |  age   |
+----------+-------+--------+
|    1     |   A1  |   1    |
|    1     |   A2  |   2    |
|    1     |   A3  |   3    |
|    2     |   B1  |   4    |
+----------+-------+--------+

在MySQL中使用以下查询，

SELECT group_id, name, COUNT(*) FROM t1 GROUP BY group_id

我们得到了，

+----------+-------+--------+----------+
| group_id |  name |  age   | COUNT(*) |
+----------+-------+--------+----------+
|    1     |   A1  |   2    |    3     |
|    2     |   B1  |   4    |    1     |
+----------+-------+--------+----------+

正如您在此处所见，值name = A1和age = 2可能不是来自同一记录。

我的问题是，如何控制显示name和age列的单个结果，因此内容来自一条记录？有没有办法以某种方式对它们进行排序？例如按年龄顺序按相反顺序排序

+----------+-------+--------+----------+
| group_id |  name |  age   | COUNT(*) |
+----------+-------+--------+----------+
|    1     |   A3  |   3    |    3     |
|    2     |   B1  |   4    |    1     |
+----------+-------+--------+----------+

感谢。

Answer 1

我不知道你为什么说你的查询有效。您还应按名称分组......

SELECT group_id, name, COUNT(*) FROM t1 GROUP BY group_id, name

如果您只想获得其中一个，请尝试：

SELECT group_id, MIN(name), COUNT(*) FROM t1 GROUP BY group_id

Answer 2

SELECT group_id, name, COUNT(*)
FROM t1 
WHERE name IN ( 'xxx', 'yyy', ..., 'zzz' )
GROUP BY group_id
SORT BY COUNT(*)

Answer 3

我不知道完全控制，但你可以这样做

SELECT student_name, MIN(test_score), MAX(test_score)
        FROM student
        GROUP BY student_name;

对GROUP BY agregats进行排序

3 个答案: