如何在不选择ORDER BY字段的情况下选择DISTINCT行 [英] How to select DISTINCT rows without having the ORDER BY field selected

问题描述

因此，我有两个表格学生(PK sID)和导师(PK pID).此查询

So I have two tables students (PK sID) and mentors (PK pID). This query

SELECT s.pID
FROM students s JOIN mentors m ON s.pID = m.pID
WHERE m.tags LIKE '%a%'
ORDER BY s.sID DESC;

提供此结果

pID
-------------
9
9
3
9
3
9
9
9
10
9
3
10  etc...

我正在尝试以此顺序获取不同导师ID的列表，因此我正在寻找要生成的SQL

I am trying to get a list of distinct mentor ID's with this ordering so I am looking for the SQL to produce

pID
-------------
9
3
10

如果仅在SELECT子句中插入DISTINCT，则会得到意外的结果10、9、3(顺序错误).任何帮助表示赞赏.

If I simply insert a DISTINCT in the SELECT clause I get an unexpected result of 10, 9, 3 (wrong order). Any help much appreciated.

推荐答案

SELECT s.pID
FROM students s JOIN mentors m ON s.pID = m.pID   
WHERE m.tags LIKE '%a%'
GROUP BY s.pID
ORDER BY MAX(s.sID) DESC

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