在Oracle中不参考双重表就从中选择吗? [英] Select from nothing in Oracle without referencing the dual table?

问题描述

在引用双重表时(例如，

selecting from nothing in Oracle SQL happens while referencing the dual table, like

SELECT sysdate FROM dual;

现在，我希望有一个对PostgreSQL也适用的查询，但是不可能从双查询中进行选择.我知道我可以删除整个FROM部分，但是在Oracle中将无法使用.

Now I'd like to have a query that also works for PostgreSQL, but selecting from dual there isn't possible. I know that I can drop the whole FROM part, but then it won't work in Oracle.

我也尝试过类似SELECT CURRENT_TIMESTAMP FROM VALUES(1)) V(C);之类的事情，但是Oracle也无法做到这一点.

I've also tried things like SELECT CURRENT_TIMESTAMP FROM VALUES(1)) V(C);, but Oracle can't do this, either.

那么有没有一种方法可以在不使用Oracle SQL中的dual表的情况下从任何地方进行选择?

So is there a way to select from nowhere without using the dual table in Oracle SQL?

推荐答案

或者，在Postgres中创建一个名为dual的表，该表由1行1列组成

Alternatively, create a table named dual in Postgres, made of 1 row and 1 column

create table dual as (select 1);

，您可以像在Oracle中那样在Postgres中使用它

and you can use it in Postgres as you would in Oracle

select 'whatever' from dual;
 ?column?
-----------
 whatever

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