>>Yes, very simple...
>>
>>

>>SELECT Client.Numero
>> FROM Client
>> LEFT JOIN Invoice ON Invoice.Numero=Client.NoInvoice AND Invoice.SecondCondition=True
>> LEFT JOIN Inventory ON Inventory.Numero=Client.NoInventory AND Inventory.SecondCondition=True
>>WHERE Invoice.Numero IS NOT NULL OR Inventory.Numero IS NOT NULL
>>

>
>This does not work.

Are you sure? I know that such queries can surprise me, but I cannot see what can go wrong here.
If you look at the output do you see repeats of the invoice table or inventory table?

I wonder whether the problem is in the description of what you are expecting.

Walter,