On Thu, Feb 28, 2008 at 1:11 AM, Helen Borrie <helebor@...> wrote:

> Erm, not so. UNION is often used - perhaps even *most often* used - to draw
> a set from a single table. Typically this will be where you want different
> information from a row depending on some condition that is determined by
> some control value. For a union the engine doesn't care where the data comes
> from, as long as the second and subsequent subsets match type-for-type.

Hmm.... ok. We are constantly learning new things. But, to be honest
with you, this is the first time I hear this. All the literature I
have read so far says the exact same thing: that unions are used to
draw data from two or more tables. And I have never come across an
example that shows that. So, if it is not asking too much, could you
please provide me with an example with a case where this would happen?

Thanks in advance,

Fidel.