我想使用orderby子句构造一个查询。请指教

Question

我的数据是这样的：

App ID Ref Id App Type Reg Date 
1  1  Main  2017-05-13 
2  2  Sub  2017-05-14 
3  1  Sub  2017-05-16 
4  2  Main  2017-05-15 
5  3  Main  2017-05-14 
6  1  sub  2017-05-17 

我想改变这个表，如下图所示。

App ID Ref Id App Type Reg Date 
4  2  Main  2017-05-15 
2  2  Sub  2017-05-14 
5  3  Main  2017-05-14 
1  1  Main  2017-05-13 
6  1  sub  2017-05-17 
3  1  Sub  2017-05-16 

显示具有相同参考ID的内容，并且具有Main的内容位于顶部。 最近注册的内容必须位于顶部。 也就是说，我想创建一个层次结构。

Select * 
from table 
order by refId desc, App Type asc, Reg Date desc 

我应该像上面那样配置查询吗？

Answer 1

测试它：

SELECT * 
FROM t 
JOIN (SELECT `Ref Id`, MAX(`Reg Date`) AS maxdate FROM t WHERE `App Type` = 'Main' GROUP BY 1) md USING(`Ref Id`) 
ORDER BY maxdate DESC, `Ref Id`, (`App Type` = 'Main') DESC; 

+--------+--------+----------+------------+------------+ 
| Ref Id | App ID | App Type | Reg Date | maxdate | 
+--------+--------+----------+------------+------------+ 
|  2 |  4 | Main  | 2017-05-15 | 2017-05-15 | 
|  2 |  2 | Sub  | 2017-05-14 | 2017-05-15 | 
|  3 |  5 | Main  | 2017-05-14 | 2017-05-14 | 
|  1 |  1 | Main  | 2017-05-13 | 2017-05-13 | 
|  1 |  6 | sub  | 2017-05-17 | 2017-05-13 | 
|  1 |  3 | Sub  | 2017-05-16 | 2017-05-13 | 
+--------+--------+----------+------------+------------+ 

Answer 2

我想你想：

select t.* 
from t 
order by (select max(t2.regdate) from t t2 where t2.refid = t.refid) desc, 
     t.refid, 
     (t.apptype = 'Main') desc, 
     t.regdate desc;