Próbowałem zrobić dużo w CTE.
Jednak próba "ponownego zdefiniowania" zestawu zestaw wierszy jest nieco trudna. Podczas gdy zadanie jest stosunkowo łatwe przy użyciu dynamicznego SQL, który to robi, nie stwarza problemów.
Chociaż ta odpowiedź może nie być najbardziej wydajna lub prosta, lub nawet poprawna w tym sensie, że nie jest to tylko CTE, może dać innym podstawę do pracy.
Aby lepiej zrozumieć moje podejście, przeczytaj komentarze, ale warto byłoby przyjrzeć się każdemu z wyrażeń CTE po kolei, zmieniając bit kodu poniżej w głównym bloku, z komentarzem poniżej sekcji.
SELECT * FROM <CTE NAME>
Powodzenia.
IF OBJECT_ID('tempdb..#cteSchema') IS NOT NULL
DROP Table #cteSchema
GO
-- BASE CTE
;WITH cte AS(SELECT 1 AS x, 2 AS y, 3 AS z),
-- So we know what columns we have from the CTE we extract it to XML
Xml_Schema AS (SELECT CONVERT(XML,(SELECT * FROM cte FOR XML PATH(''))) AS MySchema),
-- Next we need to get a list of the columns from the CTE, by querying the XML, getting the values and assigning a num to the column
MyColumns AS (SELECT D.ROWS.value('fn:local-name(.)','SYSNAME') AS ColumnName,
D.ROWS.value('.','SYSNAME') as Value,
ROW_NUMBER() OVER (ORDER BY D.ROWS.value('fn:local-name(.)','SYSNAME')) AS Num
FROM Xml_Schema
CROSS APPLY Xml_Schema.MySchema.nodes('/*') AS D(ROWS)),
-- How many columns we have in the CTE, used a coupld of times below
ColumnStats AS (SELECT MAX(NUM) AS ColumnCount FROM MyColumns),
-- create a cartesian product of the column names and values, so now we get each column with it's possible values,
-- so {x=1, x =2, x=3, y=1, y=2, y=3, z=1, z=2, z=3} -- you get the idea.
PossibleValues AS (SELECT MyC.ColumnName, MyC.Num AS ColumnNum, MyColumns.Value, MyColumns.Num,
ROW_NUMBER() OVER (ORDER BY MyC.ColumnName, MyColumns.Value, MyColumns.Num) AS ID
FROM MyColumns
CROSS APPLY MyColumns MyC
),
-- Now we have the possibly values of each "column" we now have to concat the values together using this recursive CTE.
AllRawXmlRows AS (SELECT CONVERT(VARCHAR(MAX),'<'+ISNULL((SELECT ColumnName FROM MyColumns WHERE MyColumns.Num = 1),'')+'>'+Value) as ConcatedValue, Value,ID, Counterer = 1 FROM PossibleValues
UNION ALL
SELECT CONVERT(VARCHAR(MAX),CONVERT(VARCHAR(MAX), AllRawXmlRows.ConcatedValue)+'</'+(SELECT ColumnName FROM MyColumns WHERE MyColumns.Num = Counterer)+'><'+(SELECT ColumnName FROM MyColumns WHERE MyColumns.Num = Counterer+1)+'>'+CONVERT(VARCHAR(MAX),PossibleValues.Value)) AS ConcatedValue, PossibleValues.Value, PossibleValues.ID,
Counterer = Counterer+1
FROM AllRawXmlRows
INNER JOIN PossibleValues ON AllRawXmlRows.ConcatedValue NOT LIKE '%'+PossibleValues.Value+'%' -- I hate this, there has to be a better way of making sure we don't duplicate values....
AND AllRawXmlRows.ID <> PossibleValues.ID
AND Counterer < (SELECT ColumnStats.ColumnCount FROM ColumnStats)
),
-- The above made a list but was missing the final closing XML element. so we add it.
-- we also restict the list to the items that contain all columns, the section above builds it up over many columns
XmlRows AS (SELECT DISTINCT
ConcatedValue +'</'+(SELECT ColumnName FROM MyColumns WHERE MyColumns.Num = Counterer)+'>'
AS ConcatedValue
FROM AllRawXmlRows WHERE Counterer = (SELECT ColumnStats.ColumnCount FROM ColumnStats)
),
-- Wrap the output in row and table tags to create the final XML
FinalXML AS (SELECT (SELECT CONVERT(XML,(SELECT CONVERT(XML,ConcatedValue) FROM XmlRows FOR XML PATH('row'))) FOR XML PATH('table'))as XMLData),
-- Prepare a CTE that represents the structure of the original CTE with
DataTable AS (SELECT cte.*, XmlData
FROM FinalXML, cte)
--SELECT * FROM <CTE NAME>
-- GETS destination columns with XML data.
SELECT *
INTO #cteSchema
FROM DataTable
DECLARE @XML VARCHAR(MAX) ='';
SELECT @Xml = XMLData FROM #cteSchema --Extract XML Data from the
ALTER TABLE #cteSchema DROP Column XMLData -- Removes the superflous column
DECLARE @h INT
EXECUTE sp_xml_preparedocument @h OUTPUT, @XML
SELECT *
FROM OPENXML(@h, '/table/row', 2)
WITH #cteSchema -- just use the #cteSchema to define the structure of the xml that has been constructed
EXECUTE sp_xml_removedocument @h
Tylko z jednym rzędem danych? –
@RaduGheorghiu Tak. to jest nasienie. –
Dla 3 elementów można to zrobić stosunkowo łatwo, ale jest to specyficzne dla 3 elementów. Czy potrzebujesz tylko 3 element jeden lub szukasz rozwiązania, które skaluje się? –