>UPDATE Relation SET NoField  = CASE WHEN Field = Field.Field
>                                         THEN Field.Numero
>                                    ELSE NoField END,
>                    NoField2 = CASE WHEN Field = Field.Field2
>                                        THEN Field.Numero
>                                   ELSE NoField2 END
>FROM Relation
>INNER JOIN Field ON (Ralation.Field = Field.Field OR Relation.Field2 = Field.Field2)
>