Function count_tree

datafusion-examples/examples/sql_ops/analysis.rs:269–315

Count the entire join tree and return its inputs using TreeNode API For example, if this function receives following plan: ```text JOIN / \ A GROUP | JOIN / \ B C ``` It will return `(1, [A, GROUP])`

(join: &LogicalPlan)

///
/// It will return `(1, [A, GROUP])`
fn count_tree(join: &LogicalPlan) -> (usize, Vec<&LogicalPlan>) {
    let mut inputs = Vec::new();
    let mut total = 0;

    join.apply(|node| {
        // Some extra knowledge:
        //
        // optimized plans have their projections pushed down as far as
        // possible, which sometimes results in a projection going in between 2
        // subsequent joins giving the illusion these joins are not "related",
        // when in fact they are.
        //
        // This plan:
        //   JOIN
        //   /  \
        // A   PROJECTION
        //        |
        //       JOIN
        //       /  \
        //      B    C
        //
        // is the same as:
        //
        //   JOIN
        //   /  \
        // A   JOIN
        //     /  \
        //    B    C
        // we can continue the recursion in this case
        if let LogicalPlan::Projection(_) = node {
            return Ok(TreeNodeRecursion::Continue);
        }

        // any join we count
        if matches!(node, LogicalPlan::Join(_)) {
            total += 1;
            Ok(TreeNodeRecursion::Continue)
        } else {
            inputs.push(node);
            // skip children of input node
            Ok(TreeNodeRecursion::Jump)
        }
    })
    .unwrap();

    (total, inputs)
}