>Many thanks to all who replied.
>
>To summarize the responses............
>
>When I have
>
>SELECT fields FROM yyy LEFT JOIN xxx ON condition
>
>and later have a WHERE clause involving a field in yyy
>it essentially turns the query into an INNER JOIN
>
>is this right?

RIGHT!!!!!!!!!!!!!!!!!!!

You got it!!!!!!!!!!!!!!!

UPDATE.

Now after reviewing Borislav's response I see I didn't pay enough attention.

Only if you reference XXX table in the WHERE the query will act as an INNER JOIN.