从同一个表中选择多个列而不使用表联合(Select multiple columns from the same table without tables union)

从同一个表中选择多个列而不使用表联合(Select multiple columns from the same table without tables union)

我想创建一个查询来从表中选择几个列，并将结果显示为单个列。 我知道我可以使用此查询执行此操作：

select a from Z union select b from Z union select c from Z union select d from Z ....

但在我的情况下，表Z是一个约50行的子查询，我不想复制和粘贴。 所以我想在Z只出现一次的查询中有这个。 我不知道这是否可行。

你知道这样做的方法吗？

先谢谢你。

问候。

I would like to create a query to select several columns from a table, and show the results as a single column. I know I can do this with this query:

select a from Z union select b from Z union select c from Z union select d from Z ....

But in my case, table Z is a sub-query of about 50 lines, that I would not want to copy and paste. So I would like to have this in a query where Z appears only once. I don't know if this is possible.

Do you know a way to do that?

Thank you in advance.

Regards.

最满意答案

您可以使用WITH子句来完成它：

with Z as ( select ... from ... -- <<== Put your big query here ) select a from Z union select b from Z union select c from Z union select d from Z

顶部的with子句使Z可用于查询的其余部分，而不必重复自己。

这是sqlfiddle上的一个演示 。

You can do it using a WITH clause:

with Z as ( select ... from ... -- <<== Put your big query here ) select a from Z union select b from Z union select c from Z union select d from Z

The with clause at the top makes Z available to the remaining parts of your query without having to repeat yourself.

Here is a demo on sqlfiddle.