simpledb.query
Class SelectScan

java.lang.Object
  simpledb.query.SelectScan

All Implemented Interfaces:

Scan, UpdateScan

public class SelectScan
extends Object
implements UpdateScan

The scan class corresponding to the select relational algebra operator. All methods except next delegate their work to the underlying scan.

Author:

Edward Sciore

Constructor Summary

SelectScan(Scan s, Predicate pred)
Creates a select scan having the specified underlying scan and predicate.

Method Summary

void	beforeFirst() Positions the scan before its first record.
void	close() Closes the scan and its subscans, if any.
void	delete() Deletes the current record from the scan.
int	getInt(String fldname) Returns the value of the specified integer field in the current record.
RID	getRid() Returns the RID of the current record.
String	getString(String fldname) Returns the value of the specified string field in the current record.
Constant	getVal(String fldname) Returns the value of the specified field in the current record.
boolean	hasField(String fldname) Returns true if the scan has the specified field.
void	insert() Inserts a new record somewhere in the scan.
void	moveToRid(RID rid) Positions the scan so that the current record has the specified RID.
boolean	next() Move to the next record satisfying the predicate.
void	setInt(String fldname, int val) Modifies the field value of the current record.
void	setString(String fldname, String val) Modifies the field value of the current record.
void	setVal(String fldname, Constant val) Modifies the field value of the current record.

Methods inherited from class java.lang.Object

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

Constructor Detail

SelectScan

public SelectScan(Scan s,
                  Predicate pred)

Creates a select scan having the specified underlying scan and predicate.

Parameters:

s - the scan of the underlying query

pred - the selection predicate

Method Detail

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()

Move to the next record satisfying the predicate. The method repeatedly calls next on the underlying scan until a suitable record is found, or the underlying scan contains no more records.

Specified by:

next in interface Scan

Returns:

false if there is no next record

See Also:

Scan.next()

close

public void close()

Description copied from interface: Scan

Closes the scan and its subscans, if any.

Specified by:

close in interface Scan

getVal

public Constant getVal(String fldname)

Description copied from interface: Scan

Returns the value of the specified field in the current record. The value is expressed as a Constant.

Specified by:

getVal in interface Scan

Parameters:

fldname - the name of the field

Returns:

the value of that field, expressed as a Constant.

getInt

public int getInt(String fldname)

Description copied from interface: Scan

Returns the value of the specified integer field in the current record.

Specified by:

getInt in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's integer value in the current record

getString

public String getString(String fldname)

Description copied from interface: Scan

Returns the value of the specified string field in the current record.

Specified by:

getString in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's string value in the current record

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

setVal

public void setVal(String fldname,
                   Constant val)

Description copied from interface: UpdateScan

Modifies the field value of the current record.

Specified by:

setVal in interface UpdateScan

Parameters:

fldname - the name of the field

val - the new value, expressed as a Constant

setInt

public void setInt(String fldname,
                   int val)

Description copied from interface: UpdateScan

Modifies the field value of the current record.

Specified by:

setInt in interface UpdateScan

Parameters:

fldname - the name of the field

val - the new integer value

setString

public void setString(String fldname,
                      String val)

Description copied from interface: UpdateScan

Modifies the field value of the current record.

Specified by:

setString in interface UpdateScan

Parameters:

fldname - the name of the field

val - the new string value

delete

public void delete()

Description copied from interface: UpdateScan

Deletes the current record from the scan.

Specified by:

delete in interface UpdateScan

insert

public void insert()

Description copied from interface: UpdateScan

Inserts a new record somewhere in the scan.

Specified by:

insert in interface UpdateScan

getRid

public RID getRid()

Description copied from interface: UpdateScan

Returns the RID of the current record.

Specified by:

getRid in interface UpdateScan

Returns:

the RID of the current record

moveToRid

public void moveToRid(RID rid)

Description copied from interface: UpdateScan

Positions the scan so that the current record has the specified RID.

Specified by:

moveToRid in interface UpdateScan

Parameters:

rid - the RID of the desired record