Function apply_limit

nodedb-sql/src/planner/select/entry.rs:336–392

Apply LIMIT and OFFSET to a plan.

(mut plan: SqlPlan, limit_clause: &Option<ast::LimitClause>)

/// Apply LIMIT and OFFSET to a plan.
fn apply_limit(mut plan: SqlPlan, limit_clause: &Option<ast::LimitClause>) -> SqlPlan {
    let (limit_val, offset_val) = match limit_clause {
        None => (None, 0usize),
        Some(ast::LimitClause::LimitOffset { limit, offset, .. }) => {
            let lv = limit
                .as_ref()
                .and_then(crate::coerce::expr_as_usize_literal);
            let ov = offset
                .as_ref()
                .and_then(|o| crate::coerce::expr_as_usize_literal(&o.value))
                .unwrap_or(0);
            (lv, ov)
        }
        Some(ast::LimitClause::OffsetCommaLimit { offset, limit }) => {
            let lv = crate::coerce::expr_as_usize_literal(limit);
            let ov = crate::coerce::expr_as_usize_literal(offset).unwrap_or(0);
            (lv, ov)
        }
    };

    match plan {
        SqlPlan::Scan {
            ref mut limit,
            ref mut offset,
            ..
        } => {
            *limit = limit_val;
            *offset = offset_val;
        }
        SqlPlan::Aggregate {
            limit: ref mut l, ..
        } => {
            if let Some(lv) = limit_val {
                *l = lv;
            }
        }
        SqlPlan::VectorSearch {
            top_k: ref mut k,
            ef_search: ref mut ef,
            ann_options: ref opts,
            ..
        } => {
            // Fused VectorSearch (e.g. ORDER BY vector_distance + JOIN
            // ARRAY_SLICE) inherits its outer LIMIT here. Without this,
            // a join-derived VectorSearch carries the join's default
            // 10000 limit instead of the user's `LIMIT N`.
            if let Some(lv) = limit_val {
                *k = lv;
                *ef = opts
                    .ef_search_override
                    .unwrap_or(lv * DEFAULT_EF_SEARCH_MULTIPLIER);
            }
        }
        _ => {}
    }
    plan
}