org.vanilladb.core.query.algebra

Class ProjectPlan

java.lang.Object

org.vanilladb.core.query.algebra.ProjectPlan

All Implemented Interfaces:

Plan

public class ProjectPlan
extends Object
implements Plan

The Plan class corresponding to the project relational algebra operator.

Constructor Summary

Constructors

Constructor and Description
ProjectPlan(Plan p, Set<String> fldNames) Creates a new project node in the query tree, having the specified subquery and field list.

Method Summary

Modifier and Type	Method and Description
long	blocksAccessed() Estimates the number of block accesses in the projection, which is the same as in the underlying query.
Histogram	histogram() Returns the histogram that approximates the join distribution of the field values of query results.
Scan	open() Creates a project scan for this query.
static Histogram	projectHistogram(Histogram hist, Set<String> fldNames) Returns a histogram that approximates the join frequency distribution of the projected values from the specified histograms onto the specified fields.
long	recordsOutput() Returns an estimate of the number of records in the query's output table.
Schema	schema() Returns the schema of the projection, which is taken from the field list.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ProjectPlan

public ProjectPlan(Plan p,
                   Set<String> fldNames)

Creates a new project node in the query tree, having the specified subquery and field list.

Parameters:

p - the subquery

fldNames - the list of fields

Method Detail

projectHistogram

public static Histogram projectHistogram(Histogram hist,
                                         Set<String> fldNames)

Returns a histogram that approximates the join frequency distribution of the projected values from the specified histograms onto the specified fields.

Parameters:

hist - the input join distribution of field values

fldNames - the names of fields to project to

Returns:

join distribution of projected values

open

public Scan open()

Creates a project scan for this query.

Specified by:

open in interface Plan

Returns:

a scan

See Also:

Plan.open()

blocksAccessed

public long blocksAccessed()

Estimates the number of block accesses in the projection, which is the same as in the underlying query.

Specified by:

blocksAccessed in interface Plan

Returns:

the estimated number of block accesses

See Also:

Plan.blocksAccessed()

schema

public Schema schema()

Returns the schema of the projection, which is taken from the field list.

Specified by:

schema in interface Plan

Returns:

the query's schema

See Also:

Plan.schema()

histogram

public Histogram histogram()

Returns the histogram that approximates the join distribution of the field values of query results.

Specified by:

histogram in interface Plan

Returns:

the histogram

See Also:

Plan.histogram()

recordsOutput

public long recordsOutput()

Description copied from interface: Plan

Returns an estimate of the number of records in the query's output table.

Specified by:

recordsOutput in interface Plan

Returns:

the estimated number of output records

toString

public String toString()

Overrides:

toString in class Object