Please help complete TO DO in naturalJoin, package heapdb.query;

import java.util.ArrayList;

import heapdb.ITable;

import heapdb.Schema;

import heapdb.Table;

import heapdb.Tuple;

$/**$

$*$ A simple select query of the form:

$*$ select column, column, $...$ from table where condition

$*$

$*$ @author Glenn

$*$

$*/$

public class SelectQuery $\{$

private Condition cond;

private String$[]$ colNames; $//$ a value of null means return all columns of the table

$/**$

$*$ A query that contains both a where condition and a projection of columns

$*$ @param colNames are the columns to return

$*$ @param cond is the where clause

$*/$

public SelectQuery$($String$[]$ colNames, Condition cond$)\{$

this.colNames $=$ colNames;

this.cond $=$ cond;

$\}$

$/**$

$*$ A query that contains both a where condition. All columns

$*$ of the Tuples are returned.

$*$ @param cond is the where clause

$*/$

public SelectQuery$($Condition cond$)\{$

this$($null$,$ cond$)$;

$\}$

public static Table naturalJoin$($ITable table$1,$ ITable table$2)\{$

Schema resultSchema $=$ table$1.$getSchema$().$naturaljoin$($table$2.$getSchema$())$;

Table result $=$ new Table$($resultSchema$)$;

ArrayList joinColumns $=$ new ArrayList$<>()$;

$//$ TODO find the list of join column of the $2$ tables

for $($Tuple t$1$: table$1)\{$

for $($Tuple t$2$: table$2)\{$

$//$ TODO if t$1$ matches all join columns of t$2$

$//$ TODO then insert the join of t$1$ and t$2$ into

$//$ the result table

$\}$

$\}$

return result;

$\}$

public ITable eval$($ITable table$)\{$

Schema s;

$//$ if there is a projection operation, make the new schema

if $($colNames$==$null$)$ s $=$ table.getSchema$()$;

else s $=$ table.getSchema$().$project$($colNames$)$;

Table result $=$ new Table$($s$)$;

for $($Tuple t: table$)\{$

if $($cond$.$eval$($t$))\{$

result.insert$($t$.$project$($s$))$;

$\}$

$\}$

return result;

$\}$

@Override

public String toString$()\{$

String proj$\_$columns;

if $($colNames $!=$ null$)\{$

proj$\_$columns $=$ String.join$(",",$ colNames$)$;

$\}$ else $\{$

proj$\_$columns $="*"$;

$\}$

return "select $"+$ proj$\_$columns $+"$ where $"+$ cond;

$\}$

$\}$