Gregory,
Version in title says VFP9. Some behaviors of SQL are changed. 3rd would return 1 row under VFP9 and 0 under VFP6.
Cetin

>Fabio,
>
>thanks for the sequence,
>
>I am, however puzzled
>
>>>Shouldn't that be HAVING instead of WHERE ?
>>>
>>No. They are equal on this context.
>...
>>>So, since no records have (fk is null), no records will pass the WHERE clause. Look at the output of (3)
>>
>>Have you looked the (3) ? It return one row.
>
>
>Why, (vfp6 sp5) does (3) return an empty set over here and 1 row on your computer ? Something I am missing ?
>ie, HAVING = 1 row, WHERE = zero rows
>
>>>

>>>create cursor Customer (c_id I)
>>>	insert into Customer values(1)
>>>	insert into Customer values(2)
>>>	
>>>	Create cursor Orders( ord_id I, Ord_c_id I )
>>>	
>>>	insert into Orders values (22, 2)
>>>	insert into Orders values (24, 2)
>>>	
>>>	&& find customers without order(s)
>>>	
>>>	&& (1)
>>>	select	c_id ;
>>>		from Customer ;
>>>		into cursor tmp1 ;
>>>		where	( not exists ;
>>>					(select * from Orders where (Ord_c_id = c_id) ) ;
>>>				);
>>>				
>>>	brow
>>>	
>>>	&& (2) left join, with having
>>>	select	c_id, ;
>>>			ord_id ;
>>>		from Customer ;
>>>			left join Orders on (Ord_c_id = c_id) ;
>>>		into cursor tmp2 ;
>>>		having ( ord_id is null )
>>>	
>>>	brow
>>>	
>>>	
>>>	&& (3) left join, with where
>>>	select	c_id, ;
>>>			ord_id ;
>>>		from Customer ;
>>>			left join Orders on (Ord_c_id = c_id) ;
>>>		into cursor tmp3 ;
>>>		where ( ord_id is null )
>>>	
>>>	brow
>>>

>>
>>Fabio