问连接varbinary值并忽略空值？

EN

select hashbytes('SHA1', cast(a as varbinary(max))) FROM (select 0 a, null b) t

select hashbytes('SHA1', cast(a as varbinary(max)) 
    + cast(b as varbinary(max)) 
    + cast(c as varbinary(max))
FROM (select 0 a, null b, null c) t -- There may be many columns

select hashbytes('SHA1', cast(a as varbinary(max)) 
    + isnull(cast(b as varbinary(max)), 0)) 
    + isnull(cast(c as varbinary(max)), 0)) 
FROM (select 0 a, null b, null c) t