mysql - 选择表列标题作为值

Question

我有一个表格如下:

ItemNumber -- Description -- 31.03.2015 -- 31.04.2015 -- 31.05.2015 -- 31.06.2015

========= -- ======== -- ======== -- ======== -- ======== -- =========

001 ..................xyz..................null................1000...............null................null

002 ..................xya..................2000................null...............3000................null

003 ..................xyb..................null................4000...............null................5000

004 ..................xyc..................6000................7000...............null................null

005 ..................xyd..................null................8000...............9000................null

006 ..................xye..................null................10000...............null................null

===================================================================

如何编写一个查询来返回值，以便可以获得具有值(不为空)的字段的列标题，并获取该列标题，例如:

ItemNumber -- Description -- Quantity -- Date

========= -- ======== -- ====== -- ====

001.............. -- xyz........... -- 1000...... -- 04/31/2015 12:00:00 AM

002.............. -- xya........... -- 2000...... -- 03/31/2015 12:00:00 AM

002.............. -- xya........... -- 3000...... -- 05/31/2015 12:00:00 AM

003.............. -- xyb........... -- 4000...... -- 04/31/2015 12:00:00 AM

诸如此类...

抱歉，格式很糟糕，我不知道如何在没有点的情况下创建正确的间距。

Answer 1

您可以使用大量union all来做到这一点:

select t.*
from (select ItemNumber, Description, '31.03.2015' as date, `31.03.2015` as quantity
      from table
union all
      select ItemNumber, Description, '31.04.2015' as date, `31.04.2015` as quantity
      from table
      . . .
     ) t
where quantity is not null;

在 Oracle 中，您可以使用双引号而不是反引号来转义列名。

而且，如果您有大量数据，还有其他方式来表达查询，因此您只需扫描一次表。