org.vanilladb.core.query.algebra

Class ExplainScan

java.lang.Object

org.vanilladb.core.query.algebra.ExplainScan

All Implemented Interfaces:

Scan, Record

public class ExplainScan
extends Object
implements Scan

The scan class corresponding to the explain relational algebra operator.

Constructor Summary

Constructors

Constructor and Description
ExplainScan(Scan s, Schema schema, String explain) Creates a explain scan having the specified underlying query.

Method Summary

Modifier and Type	Method and Description
void	beforeFirst() Positions the scan before its first record.
void	close() Closes the scan and its subscans, if any.
Constant	getVal(String fldName) Returns the value of the specified field.
boolean	hasField(String fldname) Returns true if the scan has the specified field.
boolean	next() Moves the scan to the next record.

Methods inherited from class java.lang.Object

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

Constructor Detail

ExplainScan

public ExplainScan(Scan s,
                   Schema schema,
                   String explain)

Creates a explain scan having the specified underlying query.

Parameters:

s - the scan of the underlying query

schema - the schema of the explain result

explain - the string that explains the underlying query's planning tree

Method Detail

getVal

public Constant getVal(String fldName)

Description copied from interface: Record

Returns the value of the specified field.

Specified by:

getVal in interface Record

Parameters:

fldName - the name of the field

Returns:

the value of that field

beforeFirst

public void beforeFirst()

Description copied from interface: Scan

Positions the scan before its first record.

Specified by:

beforeFirst in interface Scan

next

public boolean next()

Description copied from interface: Scan

Moves the scan to the next record.

Specified by:

next in interface Scan

Returns:

false if there is no next record

close

public void close()

Description copied from interface: Scan

Closes the scan and its subscans, if any.

Specified by:

close in interface Scan

hasField

public boolean hasField(String fldname)

Description copied from interface: Scan

Returns true if the scan has the specified field.

Specified by:

hasField in interface Scan

Parameters:

fldname - the name of the field

Returns:

true if the scan has that field