Function evaluate_window_functions

nodedb-query/src/window/eval.rs:23–58

Evaluate window functions over sorted, partitioned rows. `rows` is the sorted result set. Each row is a `(doc_id, serde_json::Value)`. The same rows are mutated in place with window columns appended to each document. Unknown window function names must be rejected by the planner before reaching this dispatcher; an unrecognised name here is an internal bug and panics rather than silently dropping

(
    rows: &mut [(String, serde_json::Value)],
    specs: &[WindowFuncSpec],
)

/// reaching this dispatcher; an unrecognised name here is an internal bug
/// and panics rather than silently dropping the projection.
pub fn evaluate_window_functions(
    rows: &mut [(String, serde_json::Value)],
    specs: &[WindowFuncSpec],
) {
    for spec in specs {
        let partitions = build_partitions(rows, &spec.partition_by);

        for partition_indices in &partitions {
            match spec.func_name.as_str() {
                "row_number" => apply_row_number(rows, partition_indices, &spec.alias),
                "rank" => apply_rank(rows, partition_indices, &spec.alias, &spec.order_by),
                "dense_rank" => {
                    apply_dense_rank(rows, partition_indices, &spec.alias, &spec.order_by)
                }
                "ntile" => apply_ntile(rows, partition_indices, spec),
                "percent_rank" => {
                    apply_percent_rank(rows, partition_indices, &spec.alias, &spec.order_by)
                }
                "cume_dist" => {
                    apply_cume_dist(rows, partition_indices, &spec.alias, &spec.order_by)
                }
                "lag" => apply_lag(rows, partition_indices, spec),
                "lead" => apply_lead(rows, partition_indices, spec),
                "nth_value" => apply_nth_value(rows, partition_indices, spec),
                "sum" | "count" | "avg" | "min" | "max" | "first_value" | "last_value" => {
                    apply_aggregate_window(rows, partition_indices, spec)
                }
                other => {
                    unreachable!(
                        "invariant: SQL planner validates window function names before dispatch; '{other}' is unrecognized and should have been rejected at planning time"
                    )
                }
            }
        }
    }
}

#[cfg(test)]
mod tests {