LINQ&SQL查询帮助:一起对两列执行不同操作?

SELECT  DISTINCT FromLinkId, ToLinkId
FROM    mytable

为每个选择一条记录 (FromLinkId, ToLinkId) (至少 id ),假设 SQL Server :

SELECT  *
FROM    (
        SELECT  *, ROW_NUMBER() OVER (PARTITION BY FromLinkId, ToLinkId ORDER BY id) AS rn
        FROM    mytable
        ) q
WHERE   rn = 1

试试这个:

Select Distinct FromLinkId LinkId From MyTable 
Union 
Select Distinct ToLinkId LinkId From MyTable 

SELECT Name, FromLinkId, ToLinkId FROM MyTable GROUP BY FromLinkId, ToLinkId -- if there are more than one record with the same (FromLinkId, ToLinkId) pair, only one of them is displayed.

你可以这样做:

SELECT MAX(ID), MAX(Name), FromLinkID, ToLinkID FROM MyTable 
GROUP BY FromLinkID, ToLinkID

甚至:

SELECT t.* FROM
(SELECT MAX(ID) as MaxID, FromLinkID, ToLinkID FROM MyTable  
GROUP BY FromLinkID, ToLinkID) d 
LEFT JOIN MyTable t ON d.MaxID=t.ID

LINQ解决方案:

List<MyObj> distinctResults = allResults
  .GroupBy(p => new {p.FromLinkID, p.ToLinkID} )
  .Select(g => g.First())
  .ToList();

希望它能帮助别人。

Helpful related SO question.

list distinctresults=所有结果 .select(p=>新建p.fromlinkid,p.tolinkid) 区别() 。