com.hp.hpl.jena.sparql.algebra.optimize

Class TransformDistinctToReduced

java.lang.Object

com.hp.hpl.jena.sparql.algebra.TransformCopy

com.hp.hpl.jena.sparql.algebra.optimize.TransformDistinctToReduced

All Implemented Interfaces:

Transform

public class TransformDistinctToReduced
extends TransformCopy

Transforms generic DISTINCT plus ORDER BY combinations to REDUCED plus ORDER BY which typically gives better performance and memory consumption because engines have to keep less data in-memory to evaluate it.

See also TransformOrderByDistinctAppplication which is a better optimization for these kinds of queries but only applies to a limited range of queries. Where possible that optimization is applied in preference to this one.

TransformTopN covers the case of DISTINCT plus ORDER BY where there is also a LIMIT. Where possible that optimization is applied in preference to either this or TransformOrderByDistinctAppplication.

Field Summary

Fields inherited from class com.hp.hpl.jena.sparql.algebra.TransformCopy

COPY_ALWAYS, COPY_ONLY_ON_CHANGE

Constructor Summary

Constructors

Constructor and Description
TransformDistinctToReduced()

Method Summary

Methods

Modifier and Type	Method and Description
Op	transform(OpDistinct opDistinct, Op subOp)

Methods inherited from class com.hp.hpl.jena.sparql.algebra.TransformCopy

transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TransformDistinctToReduced

public TransformDistinctToReduced()

Method Detail

transform

public Op transform(OpDistinct opDistinct,
           Op subOp)

Specified by:

transform in interface Transform

Overrides:

transform in class TransformCopy