Question

这是我的问题：

SELECT DISTINCT TOP 500 
bk.firstname,
bk.surname,
bk.email,
county.region_id,
inspection.inspection_date

FROM
bken bk
LEFT OUTER JOIN county
  ON bk.county = county.code
LEFT OUTER JOIN inspection
  ON bk.inspid = inspection.inspid

WHERE
bk.firstname IS NOT NULL
AND bk.surname IS NOT NULL
AND bk.email IS NOT NULL
AND county.region_id IS NOT NULL
AND  county.region_id <> 10  
AND inspection_date > '04/01/2012 00:00:00.000'
AND inspection_date < '10/01/2012 00:00:00.000'

我的目标是获得500名不同人的样本。

不幸的是，这会返回重复的名称（虽然检查日期不同）所以我试图选择不同的姓氏，看看这是否能解决我的问题。任何人都可以帮我这样做吗？

我正在使用Microsoft SQL Server 2008。

Answer 1

使用group by：

SELECT TOP 500 
bk.firstname,
bk.surname,
bk.email,
county.region_id,
max(inspection.inspection_date)

FROM
bken bk
LEFT OUTER JOIN county
  ON bk.county = county.code
LEFT OUTER JOIN inspection
  ON bk.inspid = inspection.inspid

WHERE
bk.firstname IS NOT NULL
AND bk.surname IS NOT NULL
AND bk.email IS NOT NULL
AND county.region_id IS NOT NULL
AND  county.region_id <> 10  
AND inspection_date > '04/01/2012 00:00:00.000'
AND inspection_date < '10/01/2012 00:00:00.000'
GROUP BY 
bk.firstname,
bk.surname,
bk.email,
county.region_id

Answer 2

您必须使用inspection.inspection_date的{{1}}汇总函数，min group by而不distinct，如下所示：

SELECT TOP 500 
bk.firstname,
bk.surname,
bk.email,
county.region_id,
min(inspection.inspection_date) as inspection_date    
FROM
bken bk
LEFT OUTER JOIN county
  ON bk.county = county.code
LEFT OUTER JOIN inspection
  ON bk.inspid = inspection.inspid

WHERE
bk.firstname IS NOT NULL
AND bk.surname IS NOT NULL
AND bk.email IS NOT NULL
AND county.region_id IS NOT NULL
AND  county.region_id <> 10  
AND inspection_date > '04/01/2012 00:00:00.000'
AND inspection_date < '10/01/2012 00:00:00.000'
group by bk.firstname,
         bk.surname,
         bk.email,
         county.region_id

在一列上选择distinct

2 个答案: