Firebird Documentation Index → Firebird Null Guide → SELECT DISTINCT |
A SELECT DISTINCT statement considers all NULL
s
to be equal (NOT DISTINCT FROM each other), so if the select is on a single
column it will return at most one NULL
.
As mentioned earlier, Firebird 2.0 has a bug that causes the NULLS FIRST|LAST directive to fail under certain circumstances with SELECT DISTINCT. For more details, see the bugs list.
Firebird Documentation Index → Firebird Null Guide → SELECT DISTINCT |