sql - 如何将列转换为行或反之亦然

Question

我有两张 table

学生:

         Name       Class  Maths Science English Hindi
         Sonia        2     98     67      53     58
         Vijay        7     89     68      45     51
    Abhishek Mishra   6     87     89      52     53
         Rupal        8     74     76      59     64
         Gaurav       10    90     78      43     41

主题:

Subject  Total_Marks
Maths       100
Science     100
English     75
Hindi       75

当我选择名称 sonia 时，它应该提供以下 SQL 输出:

Subject Total_Marks Obtained Marks
Maths     100            98
Science   100            67
English    75            53
Hindi      75            58 

Answer 1

好的，不用 UNPIVOT 你也能达到想要的结果，就像这样 -

DECLARE @subject table (subject varchar(10), total_marks int)

DECLARE @student table (name varchar(100),class int,maths int, science int,english int,hindi int)


INSERT INTO @subject
    VALUES ('Maths', 100), ('Science', 100), ('English', 75), ('Hindi', 75)


INSERT INTO @student
    VALUES ('sonia', 2, 98, 67, 53, 58),
        ('vijay', 7, 89, 68, 45, 51)


SELECT ri.subject, ri.total_marks, le.val as ObtainedMarks FROM 
(
    SELECT name, class, t.sub, t.val FROM @student
    CROSS APPLY (VALUES ('maths', maths), ('science', science), ('english', english), ('hindi', hindi)) AS t(sub, val)
) le
INNER JOIN
(
    SELECT * FROM @subject
) ri
ON le.sub = ri.subject
WHERE le.name = 'sonia'

这里我使用了CROSS APPLY和VALUES子句来制作主题名称作为键、其列值作为值的键值对组合。

结果

subject  total_marks    ObtainedMarks
-------------------------------------
 Maths     100         98
 Science   100         67
 English    75         53
 Hindi      75         58