只获得重复记录的一次出现

Question

select DISTINCT a.Schooldistricttown, a.Schooldistrictnum 
from [Legacy].[dbo].[MyTables] as a

它返回：

你能告诉我如何只出现一次a.Schooldistricttown吗？ 我尝试过使用DISTINCT和GROUP BY。但它不起作用。

注意：我还需要显示两个列。

Answer 1

有两个选项，如果您在Schooldistrictnum中获得哪个值无关紧要，那么用MAX()/MIN()分组将解决此问题：

SELECT a.Schooldistricttown,MAX(a.Schooldistrictnum)
from [Legacy].[dbo].[MyTables] a
GROUP BY a.Schooldistricttown

如果您关心，请使用ROW_NUMBER()：

SELECT s.Schooldistricttown,s.Schooldistrictnum
FROM (
    SELECT a.Schooldistricttown,a.Schooldistrictnum,
           ROW_NUMBER() OVER(PARTITION BY a.Schooldistricttown ORDER BY a.<ORDER_COLUMN>) as rnk
    from [Legacy].[dbo].[MyTables]  a) s
WHERE s.rnk = 1

您需要将<ORDER_COLUMN>替换为您决定使用哪个值的实际列

Answer 2

如果您想要所有Schooldistrictnum，请使用此

  SELECT DISTINCT 
    a.Schooldistricttown,
    (
        SELECT DISTINCT 
            ina.Schooldistrictnum + ', ' AS [text()]
        FROM 
            [Legacy].[dbo].[MyTables] as ina
        WHERE
            ina.Schooldistricttown =  a.Schooldistricttown
        FOR XML PATH ('')
     ) AS Schooldistrictnum 
   FROM [Legacy].[dbo].[MyTables] as a