>>Try
>>

>>select Numero from Client where exists (select 1 from Invoice 
>>where Invoice.Numero=Client.NoInvoice AND Invoice.SecondCondition=True)
>>OR exists (select 1 from Inventory 
>>where Inventory.Numero=Client.NoInventory AND Inventory.SecondCondition=True)

>>
>>This way either of the conditions will be true.
>
>Yes, I believe this is what I posted in Message #1619009.
>
>I, however, need to keep the LEFT JOIN as I need some fields in the result from those tables.

Do you need columns from both tables in the final result?