Struct mz_transform::will_distinct::WillDistinct

pub struct WillDistinct;

Pushes down the information that a collection will be subjected to a Distinct on specific columns.

This intends to recognize idiomatic stacks of UNION from SQL, which look like Distinct over Union, potentially over other Distinct expressions. It is only able to see patterns of DISTINCT UNION DISTINCT, .. and other operators in between will prevent the necessary insight to remove the second DISTINCT.

There are other potential optimizations, for example fusing multiple reads of the same source, where distinctness may mean they could be a single read (with additional requirements).

Implementations

impl WillDistinct

fn apply(&self, expr: &mut MirRelationExpr, derived: DerivedView<'_>)

Trait Implementations

impl Debug for WillDistinct

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

Formats the value using the given formatter.

impl Default for WillDistinct

fn default() -> WillDistinct

Returns the “default value” for a type.

impl Transform for WillDistinct

fn name(&self) -> &'static str

A short string naming the transform, as it will be reported in metrics.

fn actually_perform_transform( &self, relation: &mut MirRelationExpr, ctx: &mut TransformCtx<'_>, ) -> Result<(), TransformError>

Transform a relation into a functionally equivalent relation.

fn transform( &self, relation: &mut MirRelationExpr, args: &mut TransformCtx<'_>, ) -> Result<(), TransformError>

Transforms a relation into a functionally equivalent relation.

fn debug(&self) -> String

A string describing the transform.