simpledb.query
Class ProjectPlan

java.lang.Object
  simpledb.query.ProjectPlan

All Implemented Interfaces:

Plan

public class ProjectPlan
extends Object
implements Plan

The Plan class corresponding to the project relational algebra operator.

Author:

Edward Sciore

Constructor Summary

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

Method Summary

int	blocksAccessed() Estimates the number of block accesses in the projection, which is the same as in the underlying query.
int	distinctValues(String fldname) Estimates the number of distinct field values in the projection, which is the same as in the underlying query.
Scan	open() Creates a project scan for this query.
int	recordsOutput() Estimates the number of output records in the projection, which is the same as in the underlying query.
Schema	schema() Returns the schema of the projection, which is taken from the field list.

Methods inherited from class java.lang.Object

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

Constructor Detail

ProjectPlan

public ProjectPlan(Plan p,
                   Collection<String> fieldlist)

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

Parameters:

p - the subquery

fieldlist - the list of fields

Method Detail

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 int 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()

recordsOutput

public int recordsOutput()

Estimates the number of output records in the projection, which is the same as in the underlying query.

Specified by:

recordsOutput in interface Plan

Returns:

the estimated number of output records

See Also:

Plan.recordsOutput()

distinctValues

public int distinctValues(String fldname)

Estimates the number of distinct field values in the projection, which is the same as in the underlying query.

Specified by:

distinctValues in interface Plan

Parameters:

fldname - the name of a field

Returns:

the estimated number of distinct field values in the output

See Also:

Plan.distinctValues(java.lang.String)

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()