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package simpledb;

import java.util.*;

/**

* The Join operator implements the relational join operation.

*/

public class Join extends Operator {

private static final long serialVersionUID = 1L;

DbIterator j_child1;

DbIterator j_child2;

JoinPredicate j_p;

Tuple left_tuple;

/**

* Constructor. Accepts two children to join and the predicate to join them

* on

*

* @param p

* The predicate to use to join the children

* @param child1

* Iterator for the left(outer) relation to join

* @param child2

* Iterator for the right(inner) relation to join

*/

public Join(JoinPredicate p, DbIterator child1, DbIterator child2) {

// some code goes here

j_child1 = child1;

j_child2 = child2;

j_p = p;

left_tuple = null;

}

public JoinPredicate getJoinPredicate() {

// some code goes here

return j_p;

}

/**

* @return

* the field name of join field1. Should be quantified by

* alias or table name.

* */

public String getJoinField1Name() {

// some code goes here

//TupleDesc td = j_child1.getTupleDesc();

//td.getFieldName(i)

TupleDesc td = j_child1.getTupleDesc();

String output = td.getFieldName(j_p.jp_field1);

return output;

}

/**

* @return

* the field name of join field2. Should be quantified by

* alias or table name.

* */

public String getJoinField2Name() {

// some code goes here

TupleDesc td = j_child2.getTupleDesc();

String output = td.getFieldName(j_p.jp_field2);

return output;

}

/**

* @see simpledb.TupleDesc#merge(TupleDesc, TupleDesc) for possible

* implementation logic.

*/

public TupleDesc getTupleDesc() {

// some code goes here

return TupleDesc.merge(j_child1.getTupleDesc(), j_child2.getTupleDesc());

}

public void open() throws DbException, NoSuchElementException,

TransactionAbortedException {

// some code goes here

j_child1.open();

j_child2.open();

super.open();

}

public void close() {

// some code goes here

j_child1.close();

j_child2.close();

super.close();

}

public void rewind() throws DbException, TransactionAbortedException {

// some code goes here

j_child1.rewind();

j_child2.rewind();

}

/**

* 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.

* <p>

* 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.)

* <p>

* 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}.

*

* @return The next matching tuple.

* @see JoinPredicate#filter

*/

protected Tuple fetchNext() throws TransactionAbortedException, DbException {

// some code goes here

boolean restart_row = false;

while(left_tuple != null || j_child1.hasNext())

{

if(left_tuple == null) left_tuple = j_child1.next();

if(restart_row) j_child2.rewind();

while(j_child2.hasNext())

{

Tuple right_tuple = j_child2.next();

boolean join_worked = j_p.filter(left_tuple, right_tuple);

if(join_worked)

{

TupleDesc updated_TD = TupleDesc.merge(left_tuple.getTupleDesc(), right_tuple.getTupleDesc());

Tuple updated_Tuple = new Tuple(updated_TD);

int size1 = left_tuple.getTupleDesc().numFields();

int size2 = right_tuple.getTupleDesc().numFields();

for(int i=0; i< size1; i++)

{

Field f = left_tuple.getField(i);

updated_Tuple.setField(i,f);

}

for(int i=0; i< size2; i++)

{

Field f = right_tuple.getField(i);

updated_Tuple.setField(i+size1,f);

}

return updated_Tuple;

}

}

left_tuple = null;

restart_row = true;

}

return null;

}

@Override

public DbIterator[] getChildren() {

// some code goes here

return null;

}

@Override

public void setChildren(DbIterator[] children) {

// some code goes here

}

}