ORDER BY über mehrere Spalten

-- hier mal ein Access-SQL, falls kein MSSQL griffbereit
select  name, vorname, datum1, datum2, datum3 from  (
SELECT name, vorname, datum1, datum2, datum3
                        ,  IIF( IsNull(datum1), date() + 1000 , datum1) as a
                        ,  IIF( IsNull(datum2), date() + 1000 , datum2) as b
                        ,  IIF( IsNull(datum3), date() + 1000 , datum3) as c
FROM Helmuthelmut2000
)
order by IIf( a <= b and a<= c, a, IIF( b<=a and b<=c, b,c))
;

select  name, vorname, datum1, datum2, datum3 from (
SELECT name, vorname, datum1, datum2, datum3
                        ,  coalesce(datum1, dateadd(dd,1000,getdate()) ) as a
                        ,  coalesce(datum2, dateadd(dd,1000,getdate())) as b
                        ,  coalesce(datum3, dateadd(dd,1000,getdate())) as c
FROM Helmuthelmut2000
)
order by CASE
        WHEN (a <= b and a<= c) THEN a
        WHEN ( b<=a and b<=c)  THEN b
        ELSE c
        END
;