Jim

Thank you for responding. Testing your idea indicates the only successful way to do this is to use EMPTY().

SELE ...fields... ;
FROM customers LEFT [OUTER] JOIN invoices;
ON customers.customer_id = invoices.customer_id;
WHERE invoices.order_dt BETWEEN.... ;
OR EMPTY(Invoices.Order_dt) ...

Using ISNULL() (and ISBLANK() - I'll try anything !) both fail to return all customers, the query simply reverts to an inner join.

Using EMPTY() the query continues to work as required.

BUT ... I am worried about using this in production code, I have never seen this documented anywhere, and secondly this messes up the logic of the query horribly if the field in question can sometimes be EMPTY()!

e.g. Suppose I wanted to filter the inner table on a logical flag field, my query would have read
... WHERE invoices.lPaid = .T. ...
modifying this to read
... WHERE (invoices.lPaid = .T. OR EMPTY(invoices.lPaid) ...
to make the outer join work screws up the filtering as I now get all invoices both paid and unpaid.

I'm still looking at having to use UNION's to overcome this issue unless
someone can point out a better way.

David