Question

I have a table with next structure

Id|State|Quan|SellQuan|LastId
3 |2    | 5  | 0      |2
2 |3    |10  | 5      |1
1 |3    |15  | 5      |NULL

LastId is referenced on Id field, I need calulate value on next step: take Quan from Id=3 then add all sellquan with Id referenced on previous LastId. thats meen
Id=3 – lastId = 2 => take value from Id=2 field sellquan then chek if lastId is not null
.In my ecample LastId = 1 => Take Id=1 value SellQaun
Result: 5 + 5+ 5 = 15

Answer 1

I am not really sure what you want. But I will give it a try.

First some test data:

DECLARE @tbl TABLE(Id INT,State INT,Quan INT,SellQuan INT,LastId INT)
INSERT INTO @tbl
VALUES
    (3,2,5,0,2),
    (2,3,10,5,1),
    (1,3,15,5,NULL)

Then the recursive function like this:

DECLARE @Id INT=1
;WITH CTE(Id,parentId,SellQuan,topParent)
AS
(
    SELECT
        tbl.Id,
        tbl.LastId AS parentId,
        (CASE 
            WHEN EXISTS(SELECT NULL FROM @tbl AS tbl2 WHERE tbl2.LastId=tbl.Id)
            THEN tbl.SellQuan
            ELSE tbl.Quan
        END) AS SellQuan,
        tbl.Id AS topParent
    FROM
        @tbl AS tbl
    WHERE
        tbl.Id=@Id
    UNION ALL
    SELECT
        tbl.Id,
        tbl.LastId AS parentId,
        (CASE 
            WHEN EXISTS(SELECT NULL FROM @tbl AS tbl2 WHERE tbl2.LastId=tbl.Id)
            THEN tbl.SellQuan
            ELSE tbl.Quan
        END) AS SellQuan,
        CTE.topParent AS topParent
    FROM
        @tbl AS tbl
        JOIN CTE
            ON CTE.Id=tbl.LastId
)
SELECT
    CTE.topParent AS id,
    SUM(CTE.SellQuan) AS SellQaunResult
FROM
    CTE
GROUP BY
    CTE.topParent

Hope this helps