Itu karena NULL tidak bisa disamakan dengan nilai apapun.
Nonaktifkan opsi ANSI_NULLS lalu jalankan, Anda akan melihat barisnya sekarang:
SET ANSI_NULLS OFF
select * from #foo --returns the one record we just created
select * from #foo where colA = null --does not throw an error and does not return a record! why??
select * from #foo where colA is null --returns the record drop table #foo
