simpledb.query
Class SelectPlan

java.lang.Object
  simpledb.query.SelectPlan

All Implemented Interfaces:

Plan

public class SelectPlan
extends Object
implements Plan

The Plan class corresponding to the select relational algebra operator.

Author:

Edward Sciore

Constructor Summary

SelectPlan(Plan p, Predicate pred)
Creates a new select node in the query tree, having the specified subquery and predicate.

Method Summary

int	blocksAccessed() Estimates the number of block accesses in the selection, which is the same as in the underlying query.
int	distinctValues(String fldname) Estimates the number of distinct field values in the projection.
Scan	open() Creates a select scan for this query.
int	recordsOutput() Estimates the number of output records in the selection, which is determined by the reduction factor of the predicate.
Schema	schema() Returns the schema of the selection, which is the same as in the underlying query.

Methods inherited from class java.lang.Object

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

Constructor Detail

SelectPlan

public SelectPlan(Plan p,
                  Predicate pred)

Creates a new select node in the query tree, having the specified subquery and predicate.

Parameters:

p - the subquery

pred - the predicate

Method Detail

open

public Scan open()

Creates a select 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 selection, 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 selection, which is determined by the reduction factor of the predicate.

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. If the predicate contains a term equating the specified field to a constant, then this value will be 1. Otherwise, it will be the number of the distinct values in the underlying query (but not more than the size of the output table).

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 selection, which is the same as in the underlying query.

Specified by:

schema in interface Plan

Returns:

the query's schema

See Also:

Plan.schema()