serwer sql jeden wiersz wiele kolumn w jednej kolumnie

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)

Zapytanie nr 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

Zapytanie nr 2 – ZASTOSOWANIE ZEWNĘTRZNE:

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)

Plan zapytań:

Koszt zapytania:

Wyjście:

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: W Twoim przypadku zapytanie z OUTER APPLY jest szybszy niż ROW_NUMBER rozwiązanie.