simpledb.index.query
Class IndexSelectScan

java.lang.Object
  simpledb.index.query.IndexSelectScan

All Implemented Interfaces:

Scan

public class IndexSelectScan
extends Object
implements Scan

The scan class corresponding to the select relational algebra operator.

Author:

Edward Sciore

Constructor Summary

IndexSelectScan(Index idx, Constant val, TableScan ts)
Creates an index select scan for the specified index and selection constant.

Method Summary

void	beforeFirst() Positions the scan before the first record, which in this case means positioning the index before the first instance of the selection constant.
void	close() Closes the scan by closing the index and the tablescan.
int	getInt(String fldname) Returns the value of the field of the current data record.
String	getString(String fldname) Returns the value of the field of the current data record.
Constant	getVal(String fldname) Returns the value of the field of the current data record.
boolean	hasField(String fldname) Returns whether the data record has the specified field.
boolean	next() Moves to the next record, which in this case means moving the index to the next record satisfying the selection constant, and returning false if there are no more such index records.

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexSelectScan

public IndexSelectScan(Index idx,
                       Constant val,
                       TableScan ts)

Creates an index select scan for the specified index and selection constant.

Parameters:

idx - the index

val - the selection constant

Method Detail

beforeFirst

public void beforeFirst()

Positions the scan before the first record, which in this case means positioning the index before the first instance of the selection constant.

Specified by:

beforeFirst in interface Scan

See Also:

Scan.beforeFirst()

next

public boolean next()

Moves to the next record, which in this case means moving the index to the next record satisfying the selection constant, and returning false if there are no more such index records. If there is a next record, the method moves the tablescan to the corresponding data record.

Specified by:

next in interface Scan

Returns:

false if there is no next record

See Also:

Scan.next()

close

public void close()

Closes the scan by closing the index and the tablescan.

Specified by:

close in interface Scan

See Also:

Scan.close()

getVal

public Constant getVal(String fldname)

Returns the value of the field of the current data record.

Specified by:

getVal in interface Scan

Parameters:

fldname - the name of the field

Returns:

the value of that field, expressed as a Constant.

See Also:

Scan.getVal(java.lang.String)

getInt

public int getInt(String fldname)

Returns the value of the field of the current data record.

Specified by:

getInt in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's integer value in the current record

See Also:

Scan.getInt(java.lang.String)

getString

public String getString(String fldname)

Returns the value of the field of the current data record.

Specified by:

getString in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's string value in the current record

See Also:

Scan.getString(java.lang.String)

hasField

public boolean hasField(String fldname)

Returns whether the data record 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

See Also:

Scan.hasField(java.lang.String)