รบกวนช่วยอธิบายโค๊ด function ให้หน่อยค่ะ พอดีไม่เข้าใจโค๊ดค่ะ

class MyClass{
		public function selQuery($sqlTxt){
			if(preg_match('/SELECT/', strtoupper($sqlTxt))){
				$result = mysql_query($sqlTxt);
				$num = mysql_num_rows($result);
				if($num > 0){
					$arrRec = array();
					while($rs = mysql_fetch_assoc($result)){
						array_push($arrRec,$rs);
					}
					return $arrRec;
				}else{
					echo null;
				}
			}else{
				echo null;
			}
		}

		public function query($sql){ 
			if(@mysql_query($sql))
				return true;
			else
				return false;
		}

		public function chkUniqData($tablename,$field,$data){
			$result = mysql_query("Select $field From $tablename Where $field = '$data'");
			$num = mysql_num_rows($result);
			if($num >= 1)
				return false;
			else
				return true;
		}