选择另一列报告的列的值答案

【问题标题】：select a value of a column reported by another column选择另一列报告的列的值
【发布时间】：2013-09-17 06:55:47
【问题描述】：

我有一张这样的桌子

col_name   col_white col_red col_brown col_yellow col_one col_two ....
col_white  1          
col_red              4
col_two                                                   12
....

我必须做一个选择才能得到这个结果：

col_name     col_value
col_white    1
col_red      4
col_two      12

列数是动态的。我该怎么做？

谢谢

【问题讨论】：

标签： sql sql-server select dynamic-columns

【解决方案1】：

一种方法是

select 'Col_white' as col_name, Col_white from table
union all
select 'Col_red' as col_name, Col_red from table
.
.
select 'Col_two' as col_name, Col_two from table

您可能还需要了解 UNPIVOT

【讨论】：

【解决方案2】：

select t.col_name, max(t.col_value)
from
(select col_name, col_value
from yourtable) t
group by t.col_name

【讨论】：

【解决方案3】：

这个可以试试吗？

SELECT  col_name,CASE WHEN col_name = 'col_white' THEN col_white ELSE CASE WHEN col_name = 'col_red' THEN col_red ELSE CASE WHEN col_name = 'col_two' THEN col_two END
                   END END AS test FROM dbo.Table_1

【讨论】：

【解决方案4】：

我认为动态 sql 是解决这个问题的方法。

DECLARE @SQL AS NVARCHAR(1024)
DECLARE @COL AS NVARCHAR(255)

DECLARE CUR CURSOR FAST_FORWARD FOR
SELECT  t.col_name
FROM mytable t

CREATE TABLE #TempTable(
col_name varchar(50),
col_value varchar(50))

OPEN CUR
FETCH NEXT FROM CUR INTO @COL
WHILE @@FETCH_STATUS = 0
BEGIN
    SELECT @SQL = 'INSERT INTO #TempTable SELECT COL_NAME,'+@COL+' FROM mytable where col_name='''+@COL+''''

    EXEC (@SQL)
    FETCH NEXT FROM CUR INTO @COL
END

CLOSE CUR;
DEALLOCATE CUR;

SELECT * FROM #TempTable

DROP TABLE #TempTable

【讨论】：