SQL Server CASE????й???Null?????

??????:
??????????????????????“field”?????“field”???1??NULL????1??????????0???????д????????д????????
????(CASE field
????WHEN '1' THEN '1'
????WHEN NULL THEN '1'
????ELSE '0' END
????) AS field
??????????:
??????????when null???ж??????NULL??????ж????????
????????????ε???NULL????????????????
????(CASE isnull(field??'')
????WHEN '1' THEN '1'
????WHEN '' THEN '1'
????ELSE '0' END
????) AS field
??????????when???д????
????case when field = '1' then '1' when field is null then '1' else '0' end as field