test

Students.php

class Students {

	protected $_server = 'localhost';
	protected $_username = 'username';
	protected $_password = 'password';
	protected $_database_name = 'database_name';

	public function __construct() {
		mysql_connect($this->_server, $this->_username, $this->_password);
		mysql_select_db($this->_database_name);
	}

	public function getLikedStudent() {
		$student_Ids = $this->_getLikedStudentsIds();
		return $this->_getStudents($student_Ids);
	}

	public function getLikesOfUnlikers() {
		$where = ' liked_ID NOT IN (SELECT DISTINCT(like_ID) from Likes)';
		$student_Ids = $this->_getLikedStudentsIds('like_id', $where);
		return $this->_getStudents($student_Ids);
	}

	public function getFaggots() {
		$student_Ids = $this->_getLikeAndLikersIds();
		return $this->_getStudents($student_Ids, 'NOT IN');
	}

	protected function _getLikeAndLikersIds() {
		$sql = "SELECT DISTINCT 
			least( like_ID, liked_ID ) AS least, 
			greatest( like_ID, liked_ID ) AS greatest
			FROM Likes";
		$query = mysql_query($sql);
		$likes = array();

		while ($row = mysql_fetch_array($query)) {
			if (!in_array($row['least'], $likes)) {
				$likes[] = $row['least'];
			}
			if (!in_array($row['greatest'], $likes)) {
				$likes[] = $row['greatest'];
			}
		}
		return $likes;
	}

	protected function _getStudents(array $student_Ids, $inOrNotIn = 'IN') {
		if (count($student_Ids) == 0) {
			return null;
		}
		return $this->_getStudentsByIds($student_Ids, $inOrNotIn);
	}

	protected function _getStudentsByIds(array $liked_Ids, $inOrNotIn = 'IN') {
		$ids = implode(', ', $liked_Ids);
		$sql = "SELECT name,grade from Students WHERE id {$inOrNotIn} ({$ids})";

		$query = mysql_query($sql);
		$students_grade = array();

		while ($row = mysql_fetch_array($query)) {
			$students_grade[] = array(
				'name' => $row['name'],
				'grade' => $row['grade']
			);
		}

		return $students_grade;
	}

	protected function _getLikedStudentsIds($field = 'liked_ID', $where = 1) {
		$sql = "SELECT DISTINCT({$field}) from Likes WHERE {$where}";
		$query = mysql_query($sql);

		$liked_Ids = array();
		while ($row = mysql_fetch_array($query)) {
			$liked_Ids[] = (int) $row['liked_ID'];
		}
		return $liked_Ids;
	}

}

$students = new Students();

var_dump($students->getLikedStudent());
var_dump($students->getLikesOfUnlikers());
var_dump($students->getFaggots());