module Veritas class Optimizer module Algebra # Abstract base class representing Difference optimizations class Difference < Relation::Operation::Binary # Optimize when operands are equal class EqualOperands < self include Relation::Operation::Binary::EqualOperands # A Difference with equal operands is empty # # @return [Relation::Empty] # # @api private def optimize Veritas::Relation::Empty.new(operation.header) end end # class EqualOperands # Optimize when the left operand is empty class EmptyLeft < self include Relation::Operation::Binary::EmptyLeft # A Difference with an empty left operand is empty # # @return [Relation::Empty] # # @api private def optimize left end end # class EmptyLeft # Optimize when the right operand is empty class EmptyRight < self include Relation::Operation::Binary::EmptyRight # A Difference with an empty right operand is equivalent to the left # # @return [Relation] # # @api private def optimize left end end # class EmptyRight Veritas::Algebra::Difference.optimizer = chain( EqualOperands, EmptyLeft, EmptyRight, MaterializedOperand, UnoptimizedOperand ) end # class Difference end # module Algebra end # class Optimizer end # module Veritas