如何将多个选择的结果合并为一行

Question

我有一张表格，其中包含 4 个发电机的信息。 我想将四个查询的结果放在一行中。 有没有人有建议？

SELECT  avg(KW) as GEN_101_AVG
FROM         genset WHERE     (GenSetName   like 'GEA3519') and GenDate >= '1 jan   2003    00:00:00' and GenDate < '1 feb 2003 00:00:00'

   SELECT  avg(KW) as GEN_201_AVG
FROM         genset WHERE     (GenSetName   like 'GEA3520') and GenDate >= '1 jan 2003 00:00:00' and GenDate < '1 feb 2003 00:00:00'

SELECT  avg(KW) as GEN_301_AVG
FROM         genset WHERE     (GenSetName   like 'GEA3521') and GenDate >= '1 jan 2003 00:00:00' and GenDate < '1 feb 2003 00:00:00'

SELECT  avg(KW) as GEN_401_AVG
FROM         genset WHERE     (GenSetName   like 'GEA3522') and GenDate >= '1 jan 2003 00:00:00' and GenDate < '1 feb 2003 00:00:00'

Answer 1

SELECT  (
        SELECT  avg(KW)
        FROM    genset
        WHERE   (GenSetName   like 'GEA3519')
                and GenDate >= '1 jan   2003    00:00:00'
                and GenDate < '1 feb 2003 00:00:00'
        ) AS avg_GEA3519,
        (
        SELECT  avg(KW)
        FROM    genset
        WHERE   (GenSetName   like 'GEA3520')
                and GenDate >= '1 jan   2003    00:00:00'
                and GenDate < '1 feb 2003 00:00:00'
        ) AS avg_GEA3520,
        (
        SELECT  avg(KW)
        FROM    genset
        WHERE   (GenSetName   like 'GEA3521')
                and GenDate >= '1 jan   2003    00:00:00'
                and GenDate < '1 feb 2003 00:00:00'
        ) AS avg_GEA3521,
        (
        SELECT  avg(KW)
        FROM    genset
        WHERE   (GenSetName   like 'GEA3522')
                and GenDate >= '1 jan   2003    00:00:00'
                and GenDate < '1 feb 2003 00:00:00'
        ) AS avg_GEA3522

，或者在SQL Server 2005+ ，这个：

SELECT  [GEA3519], [GEA3520], [GEA3521], [GEA3522]
FROM    (
        SELECT  GenSetName, KW
        FROM    genset
        WHERE   GenDate >= '1 Jan 2003  00:00:00'
                AND GenDate < '1 Feb 2003 00:00:00'
        ) AS q
PIVOT
(
        AVG(KW)
        FOR  GenSetName IN (['GEA3519'], ['GEA3520'], ['GEA3521'], ['GEA3522']
)

Answer 2

另外一个选择：

SELECT
     AVG(GEN_101.kw) AS GEN_101_AVG,
     AVG(GEN_201.kw) AS GEN_201_AVG,
     AVG(GEN_301.kw) AS GEN_301_AVG,
     AVG(GEN_401.kw) AS GEN_401_AVG
FROM
     Genset GEN_101
INNER JOIN Genset GEN_201 ON
     GEN_201.GenSetName = 'GEA3520' AND
     GEN_201.GenDate >= '1 jan 2003 00:00:00' AND
     GEN_201.GenDate < '1 feb 2003 00:00:00'
INNER JOIN Genset GEN_101 ON
     GEN_301.GenSetName = 'GEA3521' AND
     GEN_301.GenDate >= '1 jan 2003 00:00:00' AND
     GEN_301.GenDate < '1 feb 2003 00:00:00'
INNER JOIN Genset GEN_101 ON
     GEN_401.GenSetName = 'GEA3522' AND
     GEN_401.GenDate >= '1 jan 2003 00:00:00' AND
     GEN_401.GenDate < '1 feb 2003 00:00:00'
WHERE
     GEN_101.GenSetName = 'GEA3519' AND
     GEN_101.GenDate >= '1 jan 2003 00:00:00' AND
     GEN_101.GenDate < '1 feb 2003 00:00:00'

Answer 3

由于选择的数量限制为四个，因此一种解决方案是选择变量，然后进行最终选择。 像下面这样：

declare @var1 <TYPE>
declare @var2 <TYPE>
declare @var3 <TYPE>
declare @var4 <TYPE>

select @var1 = SELECT avg(...) ...
select @var2 = ...
select @var3 = ...
select @var4 = ...

select @var1 as ..., @var2 as ..., @var3 as ..., @var4 as ...