Re: two tables, one result set, but no join!

From: <andrewst_at_onetel.com>
Date: 1 Jun 2005 02:36:59 -0700
Message-ID: <1117618619.376185.22730@g44g2000cwa.googlegroups.com>

Paul wrote:
> andrewst_at_onetel.com wrote:
>
>
> >> >Use UNION.
>
> >> Wouldn't UNION ALL be better in case there are duplicates?
>
> >What would be the point of having duplicates?
> >What would be the point of having duplicates?
>
>
> Getting all the data?
> Getting all the data?
>
>
> The OP presumably wants to process it in some way, and may need
> duplicates, since the data is coming from two separate tables.
>
> Why have UNION ALL at all?
> Why have UNION ALL at all?

UNION ALL is there for two reasons:
1) For the cases where for some reason you DO want the answer to contain duplicates - but I can't imagine when that would be useful 2) For the cases where you KNOW there cannot be duplicates, and therefore are able to speed up the operation by skipping the de-duplication step - this can be useful

However, what you said was "Wouldn't UNION ALL be better in case there are duplicates?"

To which I suppose the answer is either "yes" if duplicates are wanted, or "no" if duplicates are possible but NOT wanted. Received on Wed Jun 01 2005 - 04:36:59 CDT