Re: Wrapping a where clause to preserve rows with nulls

"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Wednesday, December 18, 2024, Adrian Garcia Badaracco <
> adrian(at)adriangb(dot)com> wrote:
>> Is there any way to include the rows where the predicate evaluates to null
>> while still using an index?

> ... A btree index, which handles =, can’t be told to behave
> differently and so cannot fulfill your desire to produce rows where the
> stored value is null; it can only produce those equal to 5000.

Not in a single scan, no. But multiple scans are possible:

regression=# create table t (id int unique);
CREATE TABLE
regression=# explain select * from t where id = 5000 or id is null;
QUERY PLAN
------------------------------------------------------------------------------
Bitmap Heap Scan on t (cost=8.42..18.98 rows=14 width=4)
Recheck Cond: ((id IS NULL) OR (id = 5000))
-> BitmapOr (cost=8.42..8.42 rows=14 width=0)
-> Bitmap Index Scan on t_id_key (cost=0.00..4.25 rows=13 width=0)
Index Cond: (id IS NULL)
-> Bitmap Index Scan on t_id_key (cost=0.00..4.16 rows=1 width=0)
Index Cond: (id = 5000)
(7 rows)

The OP was quite unclear about what semantics he wants for
multiple-variable WHERE clauses, but maybe something like this
would work:

WHERE (original-clause) OR x IS NULL OR y IS NULL OR ...

where each variable mentioned in original-clause is allowed
to also be NULL. Or perhaps what is wanted is

WHERE (original-clause) OR (x IS NULL AND y IS NULL AND ...)

??

regards, tom lane