Cannot check for null values ​​in sql database.

Using F # query syntax, I am trying to get all records where a specific field is not null, but I cannot figure out how.

At first I tried simply:

query {
    for h in dc.Table do
    where (h.SectorId <> null)
    select h
}

      

        
        
        
      

    

But the error indicated The type 'Nullable<Guid>' does not have 'null' as a proper value. To create a null value for a Nullable type use 'System.Nullable()'.

So, replacing null

with Nullable()

as suggested, I used:

query {
    for h in dc.Table do
    where (h.SectorId <> Nullable())
    select h
}

      

        
        
        
      

    

When I use the above query in LINQPad, it doesn't retrieve any values, even though I know they exist. The problem occurs in the generated SQL:

-- Region Parameters
DECLARE @p0 UniqueIdentifier = null
-- EndRegion
SELECT [t0].[Id], [t0].[Name], [t0].[SectorId], [t0].[Blah], [t0].[Meh], [t0].[DisplayOrder]
FROM [Table] AS [t0]
WHERE [t0].[SectorId] <> @p0

      

        
        
        
      

    

Of course this won't work, because it NULL <> NULL

will always be false in SQL; where to read WHERE [t0].[SectorId] is not null

. How can I check for null in F # queries?