Struct ColumnStatistics 

pub struct ColumnStatistics {
    pub n_distinct: usize,
    pub null_count: usize,
    pub min_value: Option<SqlValue>,
    pub max_value: Option<SqlValue>,
    pub most_common_values: Vec<(SqlValue, f64)>,
    pub histogram: Option<Histogram>,
}

Statistics for a single column

Fields

n_distinct: usize

Number of distinct values (cardinality)

null_count: usize

Number of NULL values

min_value: Option<SqlValue>

Minimum value (for range queries)

max_value: Option<SqlValue>

Maximum value (for range queries)

most_common_values: Vec<(SqlValue, f64)>

Most common values with their frequencies (top 10)

histogram: Option<Histogram>

Optional histogram for improved selectivity estimation (Phase 5.1)

Implementations

impl ColumnStatistics

pub fn compute(rows: &[Row], column_idx: usize) -> Self

Compute statistics for a column by scanning all rows

pub fn compute_with_histogram( rows: &[Row], column_idx: usize, enable_histogram: bool, num_buckets: usize, bucket_strategy: BucketStrategy, ) -> Self

Compute statistics with optional histogram support

Arguments

• rows - The rows to analyze
• column_idx - Index of the column
• enable_histogram - Whether to build a histogram
• num_buckets - Number of histogram buckets (default: 100)
• bucket_strategy - Histogram bucketing strategy

pub fn estimate_eq_selectivity(&self, value: &SqlValue) -> f64

Estimate selectivity of equality predicate: col = value

Returns fraction of rows expected to match (0.0 to 1.0) Uses histogram if available for improved accuracy (Phase 5.1)

pub fn estimate_ne_selectivity(&self, value: &SqlValue) -> f64

Estimate selectivity of inequality: col != value

pub fn estimate_range_selectivity( &self, value: &SqlValue, operator: &str, ) -> f64

Estimate selectivity of range predicate: col > value or col < value

Uses histogram if available (Phase 5.1), otherwise falls back to min/max-based linear interpolation (assumes uniform distribution)

Trait Implementations

impl Clone for ColumnStatistics

fn clone(&self) -> ColumnStatistics

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ColumnStatistics

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.