feat: optimize HogQL generated OR expressions

[orian]

Follow up to: #39568

Problem

Some queries we run, that contain multiple JOIN's fail to use indices on events table. It makes them trying read multiple terabytes of data, clogging the cluster.

Internal context:
https://posthog.slack.com/archives/C019RAX2XBN/p1760353830494289

Failing query example:

EXPLAIN PLAN indexes = 1
SELECT feature AS feature, count(DISTINCT email) AS unique_users
FROM (
    SELECT ...
        FROM events LEFT OUTER JOIN (
            SELECT argMax(person_distinct_id_overrides.person_id, person_distinct_id_overrides.version) AS person_id, person_distinct_id_overrides.distinct_id AS distinct_id
            FROM person_distinct_id_overrides
            WHERE equals(person_distinct_id_overrides.team_id, 2)
            GROUP BY person_distinct_id_overrides.distinct_id 
            HAVING ifNull(equals(argMax(person_distinct_id_overrides.is_deleted, person_distinct_id_overrides.version), 0), 0) 
            SETTINGS optimize_aggregation_in_order=1) AS events__override ON equals(events.distinct_id, events__override.distinct_id)
    WHERE and(
        equals(events.team_id, 2),
        or(
            equals(events.event, '$autocapture'), 
            equals(events.event, 'drilldown')), 
        in(
            if(not(empty(events__override.distinct_id)), events__override.person_id, events.person_id), 
            (
                SELECT cohortpeople.person_id AS person_id
                FROM cohortpeople 
                WHERE <some super long expression>)),
        1, -- THIS KILLS INDEXES
        not(match(nullIf(nullIf(events.mat_pp_email, ''), 'null'), ''))
        )
    )
WHERE isNotNull(feature)
GROUP BY feature
ORDER BY unique_users DESC
LIMIT 101 OFFSET 0
SETTINGS readonly=2, max_execution_time=600, allow_experimental_object_type=1, format_csv_allow_double_quotes=0, max_ast_elements=4000000, max_expanded_ast_elements=4000000, max_bytes_before_external_group_by=0, transform_null_in=1, optimize_min_equality_disjunction_chain_length=4294967295, allow_experimental_join_condition=1;

Solution

Skip redundant parts of boolean OR expression

Optimizations:

• or(expr, 0) <=> expr
• or(expr, 0, ...) <=> or(expr, ...)
• or(expr, 1, ...) <=> 1

Example

Input HogQL:
SELECT event FROM events WHERE 1 OR 2

Before:
SELECT event FROM events WHERE and(equals(events.team_id, 2), or(1, 1)) limit 100

After:
SELECT event FROM events WHERE equals(events.team_id, 2) LIMIT 100

[posthog-bot]

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