Tuesday, 23 April 2013

SQL PARENT CHILD TREE STRUCTURE

-- DECLARE
DECLARE @Company AS TABLE(EmpID INT, ParentID INT, PersonName VARCHAR(100));

-- Insert Temp Records
INSERT INTO @Company(EmpID, ParentID, PersonName)
VALUES(1 , NULL , 'Maulik Dhorajia')
    , (2 , NULL , 'Bhavesh Gohel')
    , (3 , NULL , 'Dinesh Padhiyar')
    , (4 , 2 , 'Vijay Kumar')
    , (5 , 1 , 'Jitendra Makwana')
    , (6 , 4 , 'Jayesh Dhobi')
    , (7 , 1 , 'Shivpalsinh Jhala')
    , (8 , 5 , 'Amit Patel')
    , (9 , 3 , 'Abidali Suthar')

-- Default data

SELECT * FROM @Company;


-- Incorrect result which we usually find on Internet
;WITH CTECompany
AS
(
    SELECT EmpID, ParentID, PersonName , 0 AS HLevel
    FROM @Company
    WHERE ParentID IS NULL
   
    UNION ALL
   
    SELECT C.EmpID, C.ParentID, C.PersonName , (CTE.HLevel + 1) AS HLevel
    FROM @Company C
    INNER JOIN CTECompany CTE ON CTE.EmpID = C.ParentID
    WHERE C.ParentID IS NOT NULL
)

-- Misleading SQL
SELECT * FROM
(
    SELECT
        EmpID
        , ParentID
        , HLevel
        , (REPLICATE( '----' , HLevel ) + PersonName) AS Person
    FROM CTECompany
) AS P
ORDER BY HLevel;


-- Working Example
;WITH CTECompany
AS
(
    SELECT
        EmpID,
        ParentID,
        PersonName ,
        0 AS HLevel,
        CAST(RIGHT(REPLICATE('_',5) +  CONVERT(VARCHAR(20),EmpID),20) AS VARCHAR(MAX)) AS OrderByField
    FROM @Company
    WHERE ParentID IS NULL
   
    UNION ALL
   
    SELECT
        C.EmpID,
        C.ParentID,
        C.PersonName ,
        (CTE.HLevel + 1) AS HLevel,
        CTE.OrderByField + CAST(RIGHT(REPLICATE('_',5) +  CONVERT(VARCHAR(20),C.EmpID),20) AS VARCHAR(MAX)) AS OrderByField
    FROM @Company C
    INNER JOIN CTECompany CTE ON CTE.EmpID = C.ParentID
    WHERE C.ParentID IS NOT NULL
)

-- Working Example
SELECT
    EmpID
    , ParentID
    , HLevel
    , PersonName
    , (REPLICATE( '----' , HLevel ) + PersonName) AS Person
FROM CTECompany
ORDER BY OrderByField,PersonName;

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