Struct ColumnStatistics 

pub struct ColumnStatistics {
    pub row_count: Option<u64>,
    pub null_count: Option<u64>,
    pub min_value: Option<String>,
    pub max_value: Option<String>,
    pub distinct_count: Option<u64>,
    pub collected_at_secs: Option<u64>,
}

Optional statistics for a table column (or the whole table).

Fields

row_count: Option<u64>

Total number of rows in the table, if known.

null_count: Option<u64>

Number of null values in the column, if known.

min_value: Option<String>

String representation of the minimum value, if known.

max_value: Option<String>

String representation of the maximum value, if known.

distinct_count: Option<u64>

Number of distinct values (NDV) for the column, if known.

Drives join-order cost estimation and broadcast sizing: a column with NDV ≈ 1 is a hot join key, while a column with NDV ≈ row count is a near-unique key (build-side fan-out is high).

collected_at_secs: Option<u64>

Wall-clock Unix timestamp (seconds) when these stats were collected by ANALYZE TABLE. The CBO refuses to use stats older than stats_max_age_secs to avoid optimising against stale cardinality information.

Implementations

impl ColumnStatistics

pub fn new() -> Self

Create a new ColumnStatistics with all fields set to None.

pub fn with_row_count(self, count: u64) -> Self

Set the row count.

pub fn with_null_count(self, count: u64) -> Self

Set the null count.

pub fn with_min(self, min: impl Into<String>) -> Self

Set the minimum value.

pub fn with_max(self, max: impl Into<String>) -> Self

Set the maximum value.

pub fn with_distinct_count(self, ndv: u64) -> Self

Set the NDV (number of distinct values) for the column.

pub fn with_collected_at_secs(self, secs: u64) -> Self

Stamp the wall-clock timestamp (seconds) at which these stats were collected. Stamped by [analyze_table][crate::analyze::analyze_table] so the CBO can detect stale stats.

pub fn equality_selectivity(&self) -> Option<f64>

Selectivity of a single-point equality filter on this column.

1.0 / distinct_count when both are known; otherwise None. 0.0 when distinct_count == 0 (the column is all-null or empty).

pub fn is_fresh(&self, now_secs: u64, max_age_secs: u64) -> bool

Whether the stats are “fresh” given a current timestamp and a maximum age in seconds.

Stats without a collection timestamp are considered fresh by default (back-compat for manually-curated stats). Stats older than max_age_secs are stale.

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.

impl Default for ColumnStatistics

fn default() -> ColumnStatistics

Returns the “default value” for a type.

impl Eq for ColumnStatistics

impl PartialEq for ColumnStatistics

fn eq(&self, other: &ColumnStatistics) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for ColumnStatistics