如何根据其他列数据筛选出相似的行(在某些列上相等)

SELECT x.id,
       x.forename,
       x.surname,
       x.somedate
  FROM (SELECT t.id,
               t.forename,
               t.surname,
               t.somedate,
               ROW_NUMBER() OVER (PARTITION BY t.forename, t.surname 
                                      ORDER BY t.somedate DESC, t.id DESC) AS rank
          FROM TABLE t_ x
WHERE x.rank = 1

有风险的做法是:

  SELECT MAX(t.id) AS id,
         t.forename,
         t.surname,
         MAX(t.somedate) AS somedate
    FROM TABLE t
GROUP BY t.forename, t.surname

我倾向于对非分组值使用subselect。

SELECT Forename, Surname, 
    (SELECT TOP 1 Id FROM myTable mt WHERE mt.Forename = m.Forename AND mt.Surname = m.Surname
     ORDER BY m.SomeDate DESC) AS Id
    (SELECT TOP 1 SomeDate FROM myTable mt WHERE mt.Forename = m.Forename AND mt.Surname = m.Surname
     ORDER BY m.SomeDate DESC) AS SomeDate
FROM myTable m
GROUP BY Forename, Surname

SELECT Id, Forename, Surname, SomeDate
FROM myTable m
WHERE m.Id = (SELECT TOP 1 Id FROM myTable mt WHERE mt.Forename = m.Forename AND mt.Surname = m.Surname
    ORDER BY m.SomeDate DESC)

对于一个datatable示例,您基本上会做相同的事情。

var recs = from record in dataTable
           where record.Id == 
               (from rec in dataTable
                where rec.Forename == record.Forename && rec.Surname == record.Surname
                orderby rec.SomeDate descending
                select rec.Id).First()
           select record;