sql server en rad flera kolumner i en kolumn

DDL:

DECLARE @temp TABLE
(
      Reg_No INT
    , Student_Name VARCHAR(20)
    , Subject1 INT
    , Subject2 INT
    , Subject3 INT
    , Subject4 INT
    , Total INT
)

INSERT INTO @temp (Reg_No, Student_Name, Subject1, Subject2, Subject3, Subject4, Total)
VALUES 
    (101, 'Kevin', 85, 94, 78, 90, 347),
    (102, 'Andy ', 75, 88, 91, 78, 332)

Fråga #1 - ROW_NUMBER:

SELECT  Reg_No = CASE WHEN rn = 1 THEN t.Reg_No END
    ,   Student_Name = CASE WHEN rn = 1 THEN t.Student_Name END
    ,   t.[Subject]
    ,   Total = CASE WHEN rn = 1 THEN t.Total END
FROM (
    SELECT 
          Reg_No
        , Student_Name
        , [Subject]
        , Total 
        , rn = ROW_NUMBER() OVER (PARTITION BY Reg_No ORDER BY 1/0)
    FROM @temp
    UNPIVOT 
    (
        [Subject] FOR tt IN (Subject1, Subject2, Subject3, Subject4)
    ) unpvt
) t

Fråga #2 - YTTRE TILLÄMPNING:

SELECT t.*
FROM @temp
OUTER APPLY 
(
    VALUES 
        (Reg_No, Student_Name, Subject1, Total),
        (NULL, NULL, Subject2, NULL),
        (NULL, NULL, Subject3, NULL),
        (NULL, NULL, Subject4, NULL)
) t(Reg_No, Student_Name, [Subject], Total)

Frågeplan:

Frågekostnad:

Utdata:

Reg_No      Student_Name         Subject     Total
----------- -------------------- ----------- -----------
101         Kevin                85          347
NULL        NULL                 94          NULL
NULL        NULL                 78          NULL
NULL        NULL                 90          NULL
102         Andy                 75          332
NULL        NULL                 88          NULL
NULL        NULL                 91          NULL
NULL        NULL                 78          NULL

PS: I ditt fall fråga med OUTER APPLY är snabbare än ROW_NUMBER lösning.