SQL - Tabla SQL

<?php

include('conexion.php');

	$sql = "SELECT m.materia, m1.materia, c.carrera, '' as correlativafinal, idcorrelativa FROM correlatividades ca, materia m, materia m1, carrera c WHERE m.idmateria = ca.materia and ca.materiacorrelativa = m1.idmateria and c.idcarrera = ca.carrera ";

	$sql .= "UNION ";

	$sql .= "SELECT m.materia, '' as materia, c.carrera, m1.materia, idcorrelativa FROM correlatividades ca, materia m, materia m1, carrera c WHERE m.idmateria = ca.materia and ca.correlativafinal = m1.idmateria and c.idcarrera = ca.carrera";

	$rs = mysql_query($sql,$coneccion);

	$cantidad = mysql_num_rows($rs);

	$i=0;

	$arr = '';

	while($row=mysql_fetch_array($rs)){

		$i = $i + 1;

		$arr .= '["'.$row[0].'","'.$row[1].'","'.$row[2].'","'.$row[3].'",';

		if($cantidad==$i){

			$arr .= '"<input type=\"button\" name=\"mcorrelativa\" value=\"Modificar\" class=\"clscorrelativa\" id=\"m'.$row[4].'\">",';

			$arr .= '"<input type=\"button\" name=\"emateria\" value=\"Eliminar\" class=\"clscorrelativa\" id=\"e'.$row[4].'\">"]';

		}else{

			$arr .= '"<input type=\"button\" name=\"mcorrelativa\" value=\"Modificar\" class=\"clscorrelativa\" id=\"m'.$row[4].'\">",';

			$arr .= '"<input type=\"button\" name=\"ecorrelativa\" value=\"Eliminar\" class=\"clscorrelativa\" id=\"e'.$row[4].'\">"],';

		}

	}

	$arr = '{"aaData":['.$arr.']}';

	echo $arr;

?>