Well, there is a wrinkle: if the predicate returns `false` but one of the columns is null then the whole thing ends up `true` when I'd want it to be `false`. Say col_a = [1] and col_b = [null]:
WHERE (col_a < 1 AND col_b > 1) OR col_a IS NULL OR col_b IS NULL -> WHERE (false AND null) OR false OR true -> WHERE false OR false OR true -> true.
That's still a pretty good solution for now.
On Wed, Dec 18, 2024 at 10:41 PM Adrian Garcia Badaracco <adrian@adriangb.com> wrote:
Thank you for the great idea Tom. While yes I can't modify the original WHERE clause I do think I'll be able to introspect it or get the system generating it to tell me which columns it references and then add an OR x is NULL OR y is NULL ...
Hence why I can't really control the WHERE clause (at least not without re-implementing a bunch of finicky error prone code).
On Wed, Dec 18, 2024 at 10:38 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
"David G. Johnston" <david.g.johnston@gmail.com> writes: > On Wednesday, December 18, 2024, Adrian Garcia Badaracco < > adrian@adriangb.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 ...)
