Re: Union Clause

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 Received on Mon May 05 2008 - 08:46:35 CDT