Struct transform::union_cancel::UnionBranchCancellation

pub struct UnionBranchCancellation;

Detects an input being unioned with its negation and cancels them out

Implementations

impl UnionBranchCancellation

pub fn action(
    &self,
    relation: &mut MirRelationExpr
) -> Result<(), TransformError>

Detects an input being unioned with its negation and cancels them out

fn branch_sign(branch: &MirRelationExpr) -> bool

Returns the sign of a given union branch. The sign is true if the branch contains an odd number of Negate operators within a chain of Map, Filter and Project operators, and false otherwise.

This sign is pre-computed for all union branches in order to avoid performing expensive comparisons of branches with the same sign since they can’t possibly cancel each other.

fn compare_branches(
    relation: &MirRelationExpr,
    other: &MirRelationExpr
) -> BranchCmp

Compares two branches to check whether they produce the same results but with negated row count values, ie. one of them contains an extra Negate operator. Negate operators may appear interleaved with Map, Filter and Project operators, but these operators must appear in the same order in both branches.

Trait Implementations

impl Debug for UnionBranchCancellation

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

Formats the value using the given formatter.

impl Transform for UnionBranchCancellation

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

Transform a relation into a functionally equivalent relation.

fn debug(&self) -> String

A string describing the transform.