是否可以从子查询中获取多个值? [英] Is it possible to get multiple values from a subquery?

问题描述

有什么方法可以让子查询在oracle db中返回多个列? (我知道此特定的sql会导致错误，但它总结了我想要的内容)

Is there any way to have a subquery return multiple columns in oracle db? (I know this specific sql will result in an error, but it sums up what I want pretty well)

select
    a.x,
    ( select b.y, b.z from b where b.v = a.v),
from a

我想要这样的结果:

a.x | b.y | b.z
---------------
1   | 2   | 3

我知道可以通过联接解决此问题，但这不是我要的.

I know it is possible to solve this problem through joins, but that is not what I am asking for.

我的问题很简单，是否有办法从子查询中获取两个或多个值?也许使用双重解决方法?这样就没有实际的联接，但是每行都有一个新的子查询吗?

My Question is simply if there is any way, to get two or more values out of a subquery? Maybe some workaround using dual? So that there is NO actual join, but a new subquery for each row?

这是一个基本问题.我知道，您可以使用join解决所有这些问题.您根本不需要这样的子查询(甚至对于一列也不需要).但是他们在那里.那么我可以那样使用它们吗?还是根本不可能?

This is a principle question. You can solve all these problems using join, I know. You do not need subqueries like this at all (not even for one column). But they are there. So can I use them in that way or is it simply impossible?

推荐答案

Select子句中的子查询(如您所述)也称为标量子查询，这意味着它是一种表达形式.这意味着它只能返回一个值.

A Subquery in the Select clause, as in your case, is also known as a Scalar Subquery, which means that it's a form of expression. Meaning that it can only return one value.

恐怕您不能从单个Scalar子查询中返回多个列，不.

I'm afraid you can't return multiple columns from a single Scalar Subquery, no.

有关Oracle Scalar子查询的更多信息:

Here's more about Oracle Scalar Subqueries:

http://docs.oracle.com/cd/B19306_01/server .102/b14200/expressions010.htm#i1033549

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