Falls ich nichts übersehen habe:
WITH ranked AS (
SELECT
ChangeDate,
ColPK,
Col1,
Col2,
Col3,
Col4,
Col5,
OverallRank = ROW_NUMBER() OVER (PARTITION BY ColPK ORDER BY ChangeDate),
Col1Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col1 ORDER BY ChangeDate),
Col2Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col2 ORDER BY ChangeDate),
Col3Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col3 ORDER BY ChangeDate),
Col4Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col4 ORDER BY ChangeDate),
Col5Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col5 ORDER BY ChangeDate)
FROM AuditTable
)
, ranked2 AS (
SELECT
ChangeDate,
ColPK,
Col1,
Col2,
Col3,
Col4,
Col5,
Col1Group = RANK() OVER (PARTITION BY ColPK, Col1 ORDER BY OverallRank - Col1Rank),
Col2Group = RANK() OVER (PARTITION BY ColPK, Col2 ORDER BY OverallRank - Col2Rank),
Col3Group = RANK() OVER (PARTITION BY ColPK, Col3 ORDER BY OverallRank - Col3Rank),
Col4Group = RANK() OVER (PARTITION BY ColPK, Col4 ORDER BY OverallRank - Col4Rank),
Col5Group = RANK() OVER (PARTITION BY ColPK, Col5 ORDER BY OverallRank - Col5Rank),
Col1Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col1, OverallRank - Col1Rank ORDER BY ChangeDate),
Col2Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col2, OverallRank - Col2Rank ORDER BY ChangeDate),
Col3Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col3, OverallRank - Col3Rank ORDER BY ChangeDate),
Col4Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col4, OverallRank - Col4Rank ORDER BY ChangeDate),
Col5Rank = ROW_NUMBER() OVER (PARTITION BY ColPK, Col5, OverallRank - Col5Rank ORDER BY ChangeDate)
FROM ranked
),
unpivoted AS (
SELECT
r.ChangeTime,
r.ColPK,
x.ColName,
ColRank = CASE x.Colname
WHEN 'Col1' THEN Col1Group
WHEN 'Col2' THEN Col2Group
WHEN 'Col3' THEN Col3Group
WHEN 'Col4' THEN Col4Group
WHEN 'Col5' THEN Col5Group
END,
Value = CASE x.Colname
WHEN 'Col1' THEN CONVERT(nvarchar(100), r.Col1)
WHEN 'Col2' THEN CONVERT(nvarchar(100), r.Col2)
WHEN 'Col3' THEN CONVERT(nvarchar(100), r.Col3)
WHEN 'Col4' THEN CONVERT(nvarchar(100), r.Col4)
WHEN 'Col5' THEN CONVERT(nvarchar(100), r.Col5)
END
FROM ranked2 r
INNER JOIN (VALUES ('Col1'), ('Col2'), ('Col3'), ('Col4'), ('Col5')) x (ColName)
ON x.ColName = 'Col1' AND Col1Rank = 1
OR x.ColName = 'Col2' AND Col2Rank = 1
OR x.ColName = 'Col3' AND Col3Rank = 1
OR x.ColName = 'Col4' AND Col4Rank = 1
OR x.ColName = 'Col5' AND Col5Rank = 1
)
SELECT
new.ChangeTime,
new.ColPK,
new.ColName,
old.Value AS OldValue,
new.Value AS NewValue
FROM unpivoted new
LEFT JOIN unpivoted old
ON new.ColPK = old.ColPK
AND new.ColName = old.ColName
AND new.ColRank = old.ColRank + 1
Grundsätzlich besteht die Idee darin, zusammenhängende Gruppen identischer Werte zu ordnen und das erste Vorkommen jedes Werts auszuwählen. Dies geschieht für jede Spalte, deren Werte geprüft werden, und die Spalten werden dabei entpivotiert. Danach wird die nichtpivotierte Zeilenmenge mit sich selbst verbunden, d. h. für jeden PK- und Spaltennamen wird jede Zeile mit ihrem Vorgänger (basierend auf der Rangfolge) abgeglichen, um den alten Wert in derselben Zeile für die endgültige Ergebnismenge zu erhalten.
