使用T-SQL有效地構建DWH從父 - 子表格

Question

在過去兩天中，我一直試圖找到一個儘可能動態的高效解決方案，但我無法做到。你有沒有提示下面的例子？我嘗試了一個遞歸調用，以獲得下面的結果到目前爲止的「級別」或本機連接。

我有 「initTable」：

parent | child 
-------+------ 
    A | H 
    A | B 
    A | C 
    B | D 
    B | G 
    C | F 
    D | E 

我想有 「finalTable」：（與動態創建列 「levelX」 的bescase

level1 | level2 | level 3 | level 4 
-------+--------+---------+--------- 
    A | A | A  | H 
    A | A | C  | F 
    A | A | B  | G 
    A | B | D  | E 

嘗試＃1：遞歸方式獲得水平

問：是否有可能在遞歸過程中爲每個級別創建一列？

WITH recTable (father, child, lev) AS 
(
    SELECT 
     p1.father, 
     p1.child, 
     0 as lev 
    FROM 
     initTable AS p1 
    WHERE 
     p1.father = 'A' 

    UNION ALL 

    SELECT 
     p1.father, 
     p1.child, 
     lev+1 
    FROM 
     initTable AS p1 
    INNER JOIN 
     recTable as p2 ON p1.father = p2.child 
) 
SELECT * FROM ASD 

嘗試＃2：但 「錯誤」 訂單

在這裏，我需要填補列 「向後」 莫名其妙......

SELECT 
    p1.child AS Level 1, 
    p2.child AS Level 2, 
    p3.child AS Level 3, 
    p4.child AS Level 4 
FROM 
    initTable p1 
LEFT JOIN 
    initTable p2 ON p1.child = p2.father 
LEFT JOIN 
    initTable p3 ON p2.child = p3.father 
LEFT JOIN 
    initTable p4 ON p3.child = p4.father 
WHERE 
    p1.father= 'A' 

是否有人知道好的和有效的方法來解決這個問題？我覺得我很接近，但目前爲止我還無法解決這個問題。

Answer 1

以下是動態的，會爲你的工作，例如，以及任何與增加/減少父/子關係：

-- Get the number of required fields 

SELECT 
    parent 
    , child 
    , 1 [level] 
INTO #checking 
FROM initTable 
WHERE parent NOT IN (SELECT child FROM initTable) 
; 

WHILE EXISTS (SELECT * FROM #checking c JOIN initTable t ON c.child = t.parent) 
BEGIN 

    INSERT INTO #checking 

    SELECT 
     t.parent 
     , t.child 
     , (SELECT MAX([level]) + 1 FROM #checking) 
    FROM 
     #checking c 
     JOIN initTable t ON c.child = t.parent 
    ; 

    DELETE 
    FROM #checking 
    WHERE [level] <> (SELECT MAX([level]) FROM #checking) 
    ; 

END 
; 

DECLARE @requiredLevels int = (SELECT TOP 1 [level] + 1 FROM #checking) 
; 

DROP TABLE #checking 
; 

-- Build a dynamic statement for the SELECT fields 

DECLARE 
    @fieldSQL varchar(1000) = '' 
    , @fieldsN int = @requiredLevels 
; 

WHILE @fieldsN > 0 
BEGIN 

    IF @fieldsN > 2 
     BEGIN 

      DECLARE 
       @coalesceFields varchar(1000) = '' 
       , @coalesceN int = @fieldsN 

      WHILE @coalesceN > 1 
      BEGIN 

       IF @coalesceFields = '' 
        SET @coalesceFields = 'L' + CAST(@coalesceN AS varchar) + '.parent' 
       ELSE 
        SET @coalesceFields = @coalesceFields + ', L' + CAST(@coalesceN AS varchar) + '.parent' 
       ; 

       SET @coalesceN = @coalesceN - 1 

      END 

      SET @fieldSQL = @fieldSQL + ', COALESCE(' + @coalesceFields + ') [level ' + CAST(@requiredLevels - @fieldsN + 1 AS varchar) + ']' 

     END 
    ELSE 
     SET @fieldSQL = @fieldSQL + ', L' + CAST(@fieldsN AS varchar) + '.' + CASE WHEN @fieldsN = 1 THEN 'child' ELSE 'parent' END + ' [level ' + CAST(@requiredLevels - @fieldsN + 1 AS varchar) + ']' 
    ; 

    SET @fieldsN = @fieldsN - 1 

END 

SET @fieldSQL = SUBSTRING(@fieldSQL, 3, LEN(@fieldSQL) - 2) 

-- Build a dynamic statement for the LEFT JOINs 

DECLARE 
    @joinSQL varchar(1000) = '' 
    , @joinsN int = 2 

WHILE @joinsN <= @requiredLevels 
BEGIN 

    SET @joinSQL = @joinSQL + ' LEFT JOIN initTable L' + CAST(@joinsN AS varchar) + ' ON L' + CAST(@joinsN - 1 AS varchar) + '.' + CASE WHEN @joinsN = 2 THEN 'child' ELSE 'parent' END + ' = L' + CAST(@joinsN AS varchar) + '.child' 

    SET @joinsN = @joinsN + 1 

END 

-- Build the final SQL statement and execute 

DECLARE @SQL varchar(8000) = 
    ' 
     SELECT ' + @fieldSQL + ' 
     FROM 
      (
       SELECT child 
       FROM initTable 
       WHERE child NOT IN (SELECT parent FROM initTable) 
      ) L1' + @joinSQL 

EXEC (@SQL)