Function shrink_boundaries

datafusion/physical-expr/src/analysis.rs:237–261

If the `PropagationResult` indicates success, this function calculates the selectivity value by comparing the initial and final column boundaries. Following this, it constructs and returns a new `AnalysisContext` with the updated parameters.

(
    graph: &ExprIntervalGraph,
    mut target_boundaries: Vec<ExprBoundaries>,
    target_expr_and_indices: &[(Arc<dyn PhysicalExpr>, usize)],
)

/// Following this, it constructs and returns a new `AnalysisContext` with the
/// updated parameters.
fn shrink_boundaries(
    graph: &ExprIntervalGraph,
    mut target_boundaries: Vec<ExprBoundaries>,
    target_expr_and_indices: &[(Arc<dyn PhysicalExpr>, usize)],
) -> Result<AnalysisContext> {
    let initial_boundaries = target_boundaries.clone();
    target_expr_and_indices.iter().for_each(|(expr, i)| {
        if let Some(column) = expr.downcast_ref::<Column>()
            && let Some(bound) = target_boundaries
                .iter_mut()
                .find(|bound| bound.column.eq(column))
        {
            bound.interval = Some(graph.get_interval(*i));
        };
    });

    let selectivity = calculate_selectivity(&target_boundaries, &initial_boundaries)?;

    assert_or_internal_err!(
        (0.0..=1.0).contains(&selectivity),
        "Selectivity is out of limit: {selectivity}",
    );

    Ok(AnalysisContext::new(target_boundaries).with_selectivity(selectivity))
}

/// Returns `Some(1.0 / distinct_count)` when the filter demonstrably collapsed
/// a non-singleton interval down to a single point, i.e. an equality predicate