Basic Database Question

Title: Strange problem with charactersets

Hi I'm just about to ask a really trivial question which has never struck me before.

If i write a simple select like

select c.contentid from content c,
persusercontentassoc p,
teachercontentassoc t
where
t.contentid = c.contentid OR
p.contentid = c.contentid;

and if the table persusercontentassoc is empty no rows are returned. However, if i populate this table i get meaningful data.

So what i'm asking is if any one table in a select contains no data will the select always return no rows ?

Thanks,

Gavin

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