Re: Union Clause

On May 5, 8:46 am, Ed Prochak <edproc..._at_gmail.com> wrote:
> On May 5, 9:17 am, Mtek <m..._at_mtekusa.com> wrote:
>
>
>
> > Hi,
>
> > This is my query:
>
> > SELECT SUM(zcom) + SUM(ze) + SUM(zp)
> > FROM
> > (SELECT count(DISTINCT(email)) FROM customers_lookup) zcom
> > UNION
> > (SELECT count(DISTINCT(email)) FROM customers_lookup) ze
> > UNION
> > (SELECT count(DISTINCT(email)) zp FROM customers_lookup) zp);
>
> > Basically I want to get a count from the three tables where the email
> > address appears in ALL THREE tables. If an email does not exist in
> > all three tables, then I do not want it counted.......
>
> > I think I'm barking up the wrong tree with the query above......
>
> > John.
>
> But you show only one table in this query, customers_lookup.
>
> Here's a hint in the form of a question:
> What is the difference between the union operation and the join
> operation?
>
> hth,
> ed

Well, I figured that UNION removed duplicates. So, I was trying to get a count of the email addresses that exist in all three tables. I made a mistake in my query:

SELECT SUM(zcom) + SUM(ze) + SUM(zp)
FROM
    (SELECT count(DISTINCT(email)) FROM customers_lookup) zcom     UNION
    (SELECT count(DISTINCT(email)) FROM customers_lookup_ze) ze     UNION
    (SELECT count(DISTINCT(email)) zp FROM customers_lookup_prim) zp);

There are the three tables.

So, I only want to include emails which are in all three tables for my counts....

Thanks for the reply.

John Received on Mon May 05 2008 - 08:56:09 CDT