Coś takiego powinno być ok: UPDATE au_Allegro SET aal_description = 'a' WHERE datalength(aal_Description) = 0 AND EXISTS(SELECT au_Id FROM au__Auction WHERE au_Id = aal_Auctionid AND au_enddate < '20160101') lub po prostu: UPDATE au_Allegro SET aal_description = 'a' WHERE datalength(aal_Description) = 0