Re: NOT IN (NULL) ?

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

"Paul" <magamos(at)mail(dot)ru> writes:
> But  there  is  not  such  thing  in PostgreSQL as empty set as "IN ()" that must be
> false, because nothing element may be found in empty set.
> And  I  thought that instead of "IN ()" I could use "IN (NULL)", but I
> was failed and result was NULL and not FALSE. :(

NULL is not an alternative spelling for an empty set.

You could get an empty IN set by using a sub-select yielding no rows,
for example

regression=# select 1 in (select 1 where false);
 ?column? 
----------
 f
(1 row)

regression=# select 1 not in (select 1 where false);
 ?column? 
----------
 t
(1 row)

			regards, tom lane