SQL:Returnera revision för poster för varje kolumn

Om jag inte har missat något:

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

I grund och botten är tanken att rangordna sammanhängande grupper med identiska värden och välja första förekomster av varje värde. Det görs för varje kolumn vars värden granskas, och kolumnerna är opivoterade i processen. Efteråt sammanfogas den opivoterade raduppsättningen till sig själv, det vill säga för varje PK- och kolumnnamn matchas varje rad med sin föregångare (baserat på rankningen) för att erhålla det gamla värdet i samma rad för den slutliga resultatuppsättningen.