Function find_window_nodes_within_select

datafusion/sql/src/unparser/utils.rs:126–162

Recursively searches children of [LogicalPlan] to find Window nodes if exist prior to encountering a Join, TableScan, or a nested subquery (derived table factor). If Window node is not found prior to this or at all before reaching the end of the tree, None is returned.

(
    plan: &'a LogicalPlan,
    mut prev_windows: Option<Vec<&'a Window>>,
    already_projected: bool,
)

/// If Window node is not found prior to this or at all before reaching the end
/// of the tree, None is returned.
pub(crate) fn find_window_nodes_within_select<'a>(
    plan: &'a LogicalPlan,
    mut prev_windows: Option<Vec<&'a Window>>,
    already_projected: bool,
) -> Option<Vec<&'a Window>> {
    // Note that none of the nodes that have a corresponding node can have more
    // than 1 input node. E.g. Projection / Filter always have 1 input node.
    let input = plan.inputs();
    let input = if input.len() > 1 {
        return prev_windows;
    } else {
        input.first()?
    };

    // Window nodes accumulate in a vec until encountering a TableScan or 2nd projection
    match input {
        LogicalPlan::Window(window) => {
            prev_windows = match &mut prev_windows {
                Some(windows) => {
                    windows.push(window);
                    prev_windows
                }
                _ => Some(vec![window]),
            };
            find_window_nodes_within_select(input, prev_windows, already_projected)
        }
        LogicalPlan::Projection(_) => {
            if already_projected {
                prev_windows
            } else {
                find_window_nodes_within_select(input, prev_windows, true)
            }
        }
        LogicalPlan::TableScan(_) => prev_windows,
        _ => find_window_nodes_within_select(input, prev_windows, already_projected),
    }
}

/// Recursively identify Column expressions and transform them into the appropriate unnest expression
///