>>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.


Only if you reference XXX table FOR NOT NULL VALUES in the WHERE the query will act as an INNER JOIN.

next is not like to an INNER JOIN

...
LEFT JOIN XXX ...
WHERE XXX.field IS NULL