PHP database operation base class (singleton mode)

The database operation base class I wrote for practice includes the most basic CURD operations. It can be integrated into the framework.

// Configuration file
$db = array(
 'host'=>'localhost',
 'user'=>'root',
 'password'=>'' ,
 'database'=>'test',
)

?>
//php class
class db {
 public $conn;
 public static $sql;
 public static $instance= null;
 private function __construct(){
 require_once('db.config.php');
 $this->conn = mysql_connect($db['host'],$db['user'],$db[ 'password']);
 if(!mysql_select_db($db['database'],$this->conn)){
 echo "failed";
 };
 mysql_query('set names utf8',$this- >conn);
 }
 public static function getInstance(){
 if(is_null(self::$instance)){
 self::$instance = new db;
 }
 return self::$instance;
 }
 /**
 * Query database
*/
 public function select($table,$condition=array(),$field = array()){
 $where='';
 if(!empty($condition)){

 foreach($condition as $k=>$v){
 $where.=$k."='".$v."' and ";
 }
 $where='where '.$where . '1=1';
 }
 $fieldstr = '';
 if(!empty($field)){

 foreach($field as $k=>$v){
 $fieldstr.= $v. ',';
 }
 $fieldstr = rtrim($fieldstr,',');
 }else{
 $fieldstr = '*';
 }
 self::$sql = "select {$fieldstr} from {$ table} {$where}";
 $result=mysql_query(self::$sql,$this->conn);
 $resuleRow = array();
 $i = 0;
 while($row=mysql_fetch_assoc( $result)){
 foreach($row as $k=>$v){
 $resuleRow[$i][$k] = $v;
 }
 $i++;
 }
 return $resuleRow;
 }
 /**
 *Add a record
*/
 public function insert($table,$data){
 $values ​​= '';
 $datas = '';
 foreach($data as $k=>$v){
 $values.=$k.',';
 $datas.="'$v'".',';
 }
 $values ​​= rtrim($values,',');
 $datas = rtrim( $datas,',');
 self::$sql = "INSERT INTO {$table} ({$values}) VALUES ({$datas})";
 if(mysql_query(self::$sql)){
 return mysql_insert_id();
 }else{
 return false;
 };
 }
 /**
 * Modify a record
*/
 public function update($table,$data,$condition=array()){
 $where ='';
 if(!empty($condition)){

 foreach($condition as $k=>$v){
 $where.=$k."='".$v."' and ";
 }
 $where='where '.$where .'1=1';
 }
 $updatastr = '';
 if(!empty($data)){
 foreach($data as $k= >$v){
 $updatastr.= $k."='".$v."',";
 }
 $updatastr = 'set '.rtrim($updatastr,',');
 }
 self::$sql = "update {$table} {$updatastr} {$where}";
 return mysql_query(self::$sql);
 }
 /**
 * Delete record
*/
 public function delete($ table,$condition){
 $where='';
 if(!empty($condition)){

 foreach($condition as $k=>$v){
 $where.=$k."= '".$v."' and ";
 }
 $where='where '.$where .'1=1';
 }
 self::$sql = "delete from {$table} {$where} ";
 return mysql_query(self::$sql);

 }

 public static function getLastSql(){
 echo self::$sql;
 }



}

$db = array(
 'host'=>'localhost',
 'user'=>'root',
 'password'=>'',
 'database' =>'test',
)

?>

class db {
	public $conn;
	public static $sql;
	public static $instance=null;
	private function __construct(){
		require_once('db.config.php');
		$this->conn = mysql_connect($db['host'],$db['user'],$db['password']);
		if(!mysql_select_db($db['database'],$this->conn)){
			echo "失败";
		};
		mysql_query('set names utf8',$this->conn);
	}
	public static function getInstance(){
		if(is_null(self::$instance)){
			self::$instance = new db;
		}
		return self::$instance;
	}
	/**
 * Query database
*/
	public function select($table,$condition=array(),$field = array()){
		$where='';
		if(!empty($condition)){

			foreach($condition as $k=>$v){
				$where.=$k."='".$v."' and ";
			}
			$where='where '.$where .'1=1';
		}
		$fieldstr = '';
		if(!empty($field)){

			foreach($field as $k=>$v){
				$fieldstr.= $v.',';
			}
			 $fieldstr = rtrim($fieldstr,',');
		}else{
			$fieldstr = '*';
		}
		self::$sql = "select {$fieldstr} from {$table} {$where}";
		$result=mysql_query(self::$sql,$this->conn);
		$resuleRow = array();
		$i = 0;
		while($row=mysql_fetch_assoc($result)){
			foreach($row as $k=>$v){
				$resuleRow[$i][$k] = $v;
			}
			$i++;
		}
		return $resuleRow;
	}
	/**
 *Add a record
*/
	 public function insert($table,$data){
	 	$values = '';
	 	$datas = '';
	 	foreach($data as $k=>$v){
	 		$values.=$k.',';
	 		$datas.="'$v'".',';
	 	}
	 	$values = rtrim($values,',');
	 	$datas   = rtrim($datas,',');
	 	self::$sql = "INSERT INTO  {$table} ({$values}) VALUES ({$datas})";
		if(mysql_query(self::$sql)){
			return mysql_insert_id();
		}else{
			return false;
		};
	 }
	 /**
 * Modify a record
*/
	public function update($table,$data,$condition=array()){
		$where='';
		if(!empty($condition)){

			foreach($condition as $k=>$v){
				$where.=$k."='".$v."' and ";
			}
			$where='where '.$where .'1=1';
		}
		$updatastr = '';
		if(!empty($data)){
			foreach($data as $k=>$v){
				$updatastr.= $k."='".$v."',";
			}
			$updatastr = 'set '.rtrim($updatastr,',');
		}
		self::$sql = "update {$table} {$updatastr} {$where}";
		return mysql_query(self::$sql);
	}
	/**
 * Delete record
*/
	 public function delete($table,$condition){
	 	$where='';
		if(!empty($condition)){

			foreach($condition as $k=>$v){
				$where.=$k."='".$v."' and ";
			}
			$where='where '.$where .'1=1';
		}
		self::$sql = "delete from {$table} {$where}";
		return mysql_query(self::$sql);

	 }

	public static function getLastSql(){
		echo self::$sql;
	}



}

$db = db::getInstance();
//$list = $db->select('demo',array('name'=>'tom','password'=>'ds'),array('name','password'));
//echo $db->insert('demo',array('name'=>'最近你啦','password'=>'123'));
//echo $db->update('demo',array("name"=>'xxx',"password"=>'123'),array('id'=>1));
echo $db->delete('demo',array('id'=>'2'));
db::getLastSql();
echo "";
?>