SQL CHECK constraint issues

I'm using SQL Server 20开发者_开发技巧08 and I have a table with three columns: Length, StartTime and EndTime. I want to make a CHECK constraint on this table which says that:

if Length == NULL then
  StartTime <> NULL and EndTime <> NULL
else
  StartTime == NULL and EndTime == NULL

I've begun to try things like this:

Length == NULL AND StartTime <> NULL AND EndTime <> NULL

Obviously this is not enough, but even this simple expression will not validate. I get the error:

"Error validating 'CK_Test_Length_Or_Time'. Do you want to edit the constraint?"

Any ideas on how to go about doing this?

CHECK ([Length] IS NULL AND [StartTime] IS NOT NULL AND [EndTime] IS NOT NULL
      OR [Length] IS NOT NULL AND [StartTime] IS NULL AND [EndTime] IS NULL))

There is no == operator in SQL Server. While checking for null you have to use "is"

Please try this:

((Length is null AND starttime is not null AND endtime is not null) OR
(Length is not null AND starttime is null AND endtime is null))

HTH