[英]SQL Join on Self by Reference
I have a table called Form. 我有一个名为Form的表。 I have grossly simplified it as follows:
我已将其简化如下:
FormID Ref Premium
1 AA 1000
1 BB 900
1 CC 600
1 DD 100
2 AA 0
2 BB 0
2 CC 0
7 AA 211
7 BB 101
7 CC 300
Let's say for example that FormID = 1 corresponds to 2013 data and FormID = 7 corresponds to 2012 data (prior year). 举例来说,FormID = 1对应于2013年数据,FormID = 7对应于2012年数据(前一年)。
I want the joined data such that I expect this table out: 我想要这样的联接数据:
CurrentFormID PriorFormID Ref PremiumCurrent PremiumPrior
1 7 AA 1000 211
1 7 BB 900 101
1 7 CC 600 300
1 NULL (OR 7) DD 100 NULL (OR 0)
Essentially I need something similar to an outer join where I specify the CurrentFormID, PriorFormID as variables (ie. 1 and 7). 本质上,我需要类似于外部联接的东西,在其中我将CurrentFormID,PriorFormID指定为变量(即1和7)。 The references must be the same OR the reference in the old data must be null.
引用必须相同,或者旧数据中的引用必须为null。
This query below is a start, but I am only getting back the values that overlap (ie the References that are common in both sets. I need to also get entries where there is no reference match in the prior form. 下面的查询是一个开始,但是我只返回了重叠的值(即,两个集合中都通用的引用。我还需要获取先前形式中没有引用匹配的条目。
SELECT
*
FROM
Form X
OUTER JOIN Form Y
ON (X.FormID = @CurrentFormID AND Y.FormID = @PriorFormID) -
WHERE X.Reference = Y.Reference
ORDER BY X.Reference
I hope I have made sense. 我希望我有道理。
You should interchange the ON and WHERE clauses: 您应该互换ON和WHERE子句:
SELECT
*
FROM
Form X
OUTER JOIN Form Y
ON X.Reference = Y.Reference
WHERE X.FormID = @CurrentFormID AND (Y.FormID IS NULL OR Y.FormID = @PriorFormID)
ORDER BY X.Reference
SELECT
X.FormId AS CurrentFormId,
Y.FormId AS PriorFormId,
X.Ref,
X.Premium AS CurrentPremium,
Y.Premium AS PriorPremium
FROM
#MyTable X
LEFT JOIN
(SELECT * FROM #MyTable WHERE FormId <> @CurrentFormId) Y
ON
X.Ref = Y.Ref
WHERE
X.FormId = @CurrentFormId AND (Y.FormId = @PriorFormId OR Y.FormId IS NULL)
Alternatively, the subquery can be built like this: 另外,子查询可以这样构建:
(SELECT * FROM #MyTable WHERE FormId = @PriorFormId) Y
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