Re: Wrapping a where clause to preserve rows with nulls

I'll note that the clause is arbitrary in the sense that I don't generate
it and cannot edit it but it's basically a bunch of boolean comparisons
chained i.e. `col_a >= 1 and col_b <=5 and col_c ...` so I can in general
add an index on say col_a and it does get used.

On Wed, Dec 18, 2024 at 9:47 PM Adrian Garcia Badaracco <adrian(at)adriangb(dot)com>
wrote:

> I have a query where I have to run a where clause generated by another
> system (i.e., I can't modify that where clause. The where clause may return
> `null`, but I actually want to keep rows that return `null` (and rows that
> return `true` but not rows that return `false`).
>
> I thought it would be as simple as wrapping in `(...) is not false` but
> that seems to prevent index usage.
>
> For example, let's say that given the table:
>
> CREATE TABLE test_index (value INTEGER);
> CREATE INDEX idx_value ON test_index(value);
>
> And the predicate `value = 5000`, if I run the original query that
> excludes rows where the predicate is null it uses the index:
>
> SELECT *
> FROM test_index
> WHERE value = 5000;
>
> But as soon as I tack on an `IS NOT FALSE` the index is not used:
>
> SELECT *
> FROM test_index
> WHERE (value = 5000) IS NOT FALSE;
>
> This was surprising to me. I was hoping this might be able to use the
> index.
>
> Is there any way to include the rows where the predicate evaluates to null
> while still using an index?
>
>