OrderByDistinctOptimiser Class |
An optimizer that handles a special case for ORDER BY + DISTINCT combinations which can significantly improve performance by eliminating duplicates prior to sorting when the default SPARQL behaviour is to do a potentially costly sort over many duplicates and then eliminate distincts.
Inheritance HierarchyNamespace: VDS.RDF.Query.Optimisation
Assembly: dotNetRDF (in dotNetRDF.dll) Version:
SyntaxThe OrderByDistinctOptimiser type exposes the following members.
Constructors| Name | Description | |
|---|---|---|
 | OrderByDistinctOptimiser | Initializes a new instance of the OrderByDistinctOptimiser class |
Methods| Name | Description | |
|---|---|---|
| Equals | Determines whether the specified object is equal to the current object. (Inherited from Object.) |
 | Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
| GetHashCode | Serves as the default hash function. (Inherited from Object.) |
| GetType | Gets the Type of the current instance. (Inherited from Object.) |
| IsApplicable(SparqlQuery) |
Returns true if the query is a SELECT DISTINCT or SELECT REDUCED and has an ORDER BY.
|
| IsApplicable(SparqlUpdateCommandSet) |
Returns that this is not applicable to updates.
|
| MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
| Optimise |
Optimizes the given algebra.
|
| ToString | Returns a string that represents the current object. (Inherited from Object.) |
Remarks
Only applies to queries which meet the following criteria:.
- Has an ORDER BY and a DISTNCT on the same level of the query
- Selects a fixed list of variables i.e. not a SELECT DISTINCT *
- All variables used in the ORDER BY expressions also occur in the project list
See Also