Struct ScanArgs 

pub struct ScanArgs<'a> { /* private fields */ }

Arguments for scanning a table with TableProvider::scan_with_args.

Implementations

impl<'a> ScanArgs<'a>

pub fn with_projection(self, projection: Option<&'a [usize]>) -> Self

Set the column projection for the scan.

The projection is a list of column indices from TableProvider::schema that should be included in the scan results. If None, all columns are included.

Arguments

• projection - Optional slice of column indices to project

pub fn projection(&self) -> Option<&'a [usize]>

Get the column projection for the scan.

Returns a reference to the projection column indices, or None if no projection was specified (meaning all columns should be included).

pub fn with_filters(self, filters: Option<&'a [Expr]>) -> Self

Set the filter expressions for the scan.

Filters are boolean expressions that should be evaluated during the scan to reduce the number of rows returned. All expressions are combined with AND logic. Whether filters are actually pushed down depends on TableProvider::supports_filters_pushdown.

Arguments

• filters - Optional slice of filter expressions

pub fn filters(&self) -> Option<&'a [Expr]>

Get the filter expressions for the scan.

Returns a reference to the filter expressions, or None if no filters were specified.

pub fn with_limit(self, limit: Option<usize>) -> Self

Set the maximum number of rows to return from the scan.

If specified, the scan should return at most this many rows. This is typically used to optimize queries with LIMIT clauses.

Arguments

• limit - Optional maximum number of rows to return

pub fn limit(&self) -> Option<usize>

Get the maximum number of rows to return from the scan.

Returns the row limit, or None if no limit was specified.

pub fn with_statistics_requests( self, statistics_requests: &'a [StatisticsRequest], ) -> Self

Specifies the statistics the caller may use when optimizing the query.

This is intended to allow the TableProvider to cheaply provide statistics that may help, such as those it has in an in-memory catalog or from some other metadata source.

TableProviders read these via Self::statistics_requests(); anything a TableProvider cannot answer cheaply it simply ignores. DataFusion’s own TableProviders ignore this field — it exists so a request can be threaded from a custom optimizer rule (which annotates TableScan::statistics_requests) through to a custom TableProvider.

pub fn statistics_requests(&self) -> &'a [StatisticsRequest]

Get the statistics requests for the scan. Empty if none were set.

See Self::with_statistics_requests for more details

Trait Implementations

impl<'a> Clone for ScanArgs<'a>

fn clone(&self) -> ScanArgs<'a>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Debug for ScanArgs<'a>

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

Formats the value using the given formatter.

impl<'a> Default for ScanArgs<'a>

fn default() -> ScanArgs<'a>

Returns the “default value” for a type.