simpledb

Class Join

java.lang.Object

simpledb.Operator

simpledb.Join

All Implemented Interfaces:

java.io.Serializable, DbIterator

public class Join
extends Operator

The Join operator implements the relational join operation.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private DbIterator	child1
private DbIterator	child2
private JoinPredicate	predicate
private static long	serialVersionUID
(package private) java.util.Iterator<Tuple>	tuples

Constructor Summary

Constructors

Constructor and Description
Join(JoinPredicate predicate, DbIterator child1, DbIterator child2) Constructor.

Method Summary

Modifier and Type	Method and Description
void	close() Close iterators
protected Tuple	fetchNext() Returns the next tuple generated by the join, or null if there are no more tuples.
DbIterator[]	getChildren()
java.lang.String	getJoinField1Name()
java.lang.String	getJoinField2Name()
JoinPredicate	getJoinPredicate()
TupleDesc	getTupleDesc() Returns the TupleDesc associated with this DbIterator.
void	open() Open iterators
void	rewind() Rewind the iterators
void	setChildren(DbIterator[] children) Set the children(child) of this operator.

Methods inherited from class simpledb.Operator

getEstimatedCardinality, hasNext, next, setEstimatedCardinality

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

predicate

private JoinPredicate predicate

child1

private DbIterator child1

child2

private DbIterator child2

tuples

java.util.Iterator<Tuple> tuples

Constructor Detail

Join

public Join(JoinPredicate predicate,
            DbIterator child1,
            DbIterator child2)

Constructor. Accepts to children to join and the predicate to join them on

Parameters:

predicate - The predicate to use to join the children

child1 - Iterator for the left(outer) relation to join

child2 - Iterator for the right(inner) relation to join

Method Detail

getJoinPredicate

public JoinPredicate getJoinPredicate()

Returns:

The predicate used to join children

getJoinField1Name

public java.lang.String getJoinField1Name()

Returns:

the field name of join field1. Should be quantified by alias or table name.

getJoinField2Name

public java.lang.String getJoinField2Name()

Returns:

the field name of join field2. Should be quantified by alias or table name.

getTupleDesc

public TupleDesc getTupleDesc()

Description copied from interface: DbIterator

Returns the TupleDesc associated with this DbIterator.

Specified by:

getTupleDesc in interface DbIterator

Specified by:

getTupleDesc in class Operator

Returns:

The Tuple desc of the join

See Also:

for possible implementation logic.

open

public void open()
          throws DbException,
                 java.util.NoSuchElementException,
                 TransactionAbortedException

Open iterators

Specified by:

open in interface DbIterator

Overrides:

open in class Operator

Throws:

DbException

java.util.NoSuchElementException

TransactionAbortedException

close

public void close()

Close iterators

Specified by:

close in interface DbIterator

Overrides:

close in class Operator

rewind

public void rewind()
            throws DbException,
                   TransactionAbortedException

Rewind the iterators

Throws:

DbException

TransactionAbortedException

fetchNext

protected Tuple fetchNext()
                   throws TransactionAbortedException,
                          DbException

Returns the next tuple generated by the join, or null if there are no more tuples. Logically, this is the next tuple in r1 cross r2 that satisfies the join predicate. There are many possible implementations; the simplest is a nested loops join.

Note that the tuples returned from this particular implementation of Join are simply the concatenation of joining tuples from the left and right relation. Therefore, if an equality predicate is used there will be two copies of the join attribute in the results. (Removing such duplicate columns can be done with an additional projection operator if needed.)

For example, if one tuple is {1,2,3} and the other tuple is {1,5,6}, joined on equality of the first column, then this returns {1,2,3,1,5,6}.

Specified by:

fetchNext in class Operator

Returns:

The next matching tuple.

Throws:

TransactionAbortedException

DbException

See Also:

JoinPredicate.filter(simpledb.Tuple, simpledb.Tuple)

getChildren

public DbIterator[] getChildren()

Specified by:

getChildren in class Operator

Returns:

return the children DbIterators of this operator. If there is only one child, return an array of only one element. For join operators, the order of the children is not important. But they should be consistent among multiple calls.

setChildren

public void setChildren(DbIterator[] children)

Set the children(child) of this operator. If the operator has only one child, children[0] should be used. If the operator is a join, children[0] and children[1] should be used.

Specified by:

setChildren in class Operator

Parameters:

children - the DbIterators which are to be set as the children(child) of this operator