Function optimize_subquery_sort

datafusion/sql/src/relation/mod.rs:367–399

(
    plan: LogicalPlan,
    enable_subquery_sort_elimination: bool,
)

}

fn optimize_subquery_sort(
    plan: LogicalPlan,
    enable_subquery_sort_elimination: bool,
) -> Result<Transformed<LogicalPlan>> {
    if !enable_subquery_sort_elimination {
        return Ok(Transformed::no(plan));
    }

    // When initializing subqueries, we examine sort options since they might be unnecessary.
    // They are only important if the subquery result is affected by the ORDER BY statement,
    // which can happen when we have:
    // 1. DISTINCT ON / ARRAY_AGG ... => Handled by an `Aggregate` and its requirements.
    // 2. RANK / ROW_NUMBER ... => Handled by a `WindowAggr` and its requirements.
    // 3. LIMIT => Handled by a `Sort`, so we need to search for it.
    let mut has_limit = false;

    plan.transform_down(|c| {
        if let LogicalPlan::Limit(_) = c {
            has_limit = true;
            return Ok(Transformed::no(c));
        }
        match c {
            LogicalPlan::Sort(s) => {
                if !has_limit {
                    has_limit = false;
                    return Ok(Transformed::yes(Arc::unwrap_or_clone(s.input)));
                }
                Ok(Transformed::no(LogicalPlan::Sort(s)))
            }
            _ => Ok(Transformed::no(c)),
        }
    })
}