列入SQL Server 2005/8列

Question

我刚开始深入研究SQL Server,我遇到了问题.我必须将一行转换为一列,但我无法弄明白.

该行看起来像这样:

   Columns:      T1 T2 T3 .........T20
    Values:      1   0  9 ......... 15

我想收到这样的东西:

    Col  Val
    ________
    T1    1
    T2    0
    T3    9
    ........
    T20   15

我知道我必须使用一个支点,我已经读过这个,但无法弄明白

Answer 1

你必须使用UNPIVOT表运算符,如下所示:

SELECT col, val
FROM Tablename AS t
UNPIVOT
(
   Val
   FOR Col IN (T1, T2, ..., T20)
) AS u;

SQL小提琴演示.

更新1

如果你想为任意数量的列动态地执行此操作,而不需要手动编写它们,我能想到的唯一方法是从表中读取这些列information_schema.columns以获取表的列名列表.然后使用动态SQL动态组合语句,FOR col IN ...如下所示:

DECLARE @cols AS NVARCHAR(MAX);
DECLARE @query AS NVARCHAR(MAX);

select @cols = STUFF((SELECT distinct ',' +
                        QUOTENAME(column_name)
                      FROM information_schema.columns
                      WHERE table_name = 'tablename'
                      FOR XML PATH(''), TYPE
                     ).value('.', 'NVARCHAR(MAX)') 
                        , 1, 1, '');

SELECT @query = ' SELECT col, val
                  FROM tablename AS t
                  UNPIVOT
                  (
                  val
                  FOR col IN ( ' + @cols + ' )
                  ) AS u;';

EXECUTE(@query);

更新了SQL小提琴演示

这会给你:

| COL | VAL |
-------------
|  T1 |   1 |
| T10 |  15 |
| T11 |  33 |
| T12 |  31 |
| T13 |  12 |
| T14 |  10 |
| T15 |  12 |
| T16 |   9 |
| T17 |  10 |
| T18 |   2 |
| T19 |  40 |
|  T2 |   0 |
| T20 |  21 |
|  T3 |   9 |
|  T4 |   2 |
|  T5 |   3 |
|  T6 |  10 |
|  T7 |  14 |
|  T8 |  15 |
|  T9 |  20 |