Struct NullProvider 

pub struct NullProvider;

Provider that returns None for everything. Planner uses its built-in heuristic constants.

Trait Implementations

impl Clone for NullProvider

fn clone(&self) -> NullProvider

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for NullProvider

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

Formats the value using the given formatter.

impl Default for NullProvider

fn default() -> NullProvider

Returns the “default value” for a type.

impl StatsProvider for NullProvider

fn table_stats(&self, _table: &str) -> Option<TableStats>

Return row-count / page-count / column metadata for table, or None when stats are not available.

fn index_stats(&self, _table: &str, _column: &str) -> Option<IndexStats>

Return the IndexStats backing a secondary index on (table, column), if one exists. The planner uses IndexStats::point_selectivity to derive equality selectivity instead of the 0.01 constant.

fn column_stats(&self, table: &str, column: &str) -> Option<ColumnStats>

Return per-column statistics (distinct count, null count, min/max) when available. Default implementation derives from StatsProvider::table_stats when present.

fn has_index(&self, table: &str, column: &str) -> bool

Convenience: does a usable index exist on (table, column)?

fn distinct_values(&self, table: &str, column: &str) -> Option<u64>

Convenience: distinct-value count for a column, via column stats or an index on that column, whichever is available.

fn column_histogram(&self, _table: &str, _column: &str) -> Option<Histogram>

Optional equi-depth histogram for the column. Defaults to None, in which case the planner falls back to its uniform 0.3 range heuristic.

fn column_mcv(&self, _table: &str, _column: &str) -> Option<MostCommonValues>

Optional most-common-values list for the column. Defaults to None, in which case the planner falls back to its uniform 0.01 equality heuristic. Use for skewed columns where one or two values dominate the table.