PHP/MySQL performance question

Just had a quick question for those of you knowledgeable about performance. I have created a "MySQL" class, and every time I perform a query, I create a new MySQL object. See below

    public function get_am_sales() {
        $mysql = new MySQL();
        $mysql->connect();
        $query = "some query";
        $mysql->query($query);
        $result = $mysql->return_assoc();
        unset($mysql);
        return $result;
    }

    public function get_pm_sales() {
        $mysql = new MySQL();
        $mysql->connect();
        $query = "some query";
        $mysql->query($query);
        $result = $mysql-&开发者_JAVA百科gt;return_assoc();
        unset($mysql);
        return $result;
    }

    public function get_comp_sales() {
        $mysql = new MySQL();
        $mysql->connect();
        $query = "some query";
        $mysql->query($query);
        $result = $mysql->return_assoc();
        unset($mysql);
        return $result;
    }

$sales = new Sales();
$amSales = $sales->get_am_sales();
$pmSales = $sales->get_pm_sales();
$compSales = $sales->get_comp_sales();

The code above obviously works, but I was wondering if this is a performance hit since I open and close a connection with every function call. I have tried to implement the class using one connection, but I get errors. See below

    public function connect() {
        $this->mysql = new MySQL();
        $this->mysql->connect();
    }

    public function get_am_sales() {
        $query = "SELECT site_id, dly_sls AS am_sales, cov_cnt AS am_covers
                  FROM v_sales_yesterday
                  WHERE am_pm = 'AM'
                  GROUP BY site_id
                  ORDER BY site_id ASC";
        $this->mysql->query($query);
        $result = $this->mysql->return_assoc();
        return $result;
    }

    public function get_pm_sales() {
        $query = "SELECT site_id, dly_sls AS pm_sales, cov_cnt AS pm_covers
                  FROM v_sales_today
                  WHERE am_pm = 'PM'
                  GROUP BY site_id
                  ORDER BY site_id ASC";
        $this->mysql->query($query);
        $result = $this->mysql->return_assoc();
        return $result;
    }

    public function get_comp_sales() {
        $query = "SELECT business_date, site_id, dly_sls AS comp_sales
                  FROM v_sales_today_comp 
                  WHERE am_pm = 'PM'
                  GROUP BY site_id
                  ORDER BY site_id ASC";
        $this->mysql->query($query);
        $result = $this->mysql->return_assoc();
        return $result;
    }

    public function disconnect() {
        unset($this->mysql);
    }

$sales = new Sales();
$sales->connect();
$amSales = $sales->get_am_sales();
$pmSales = $sales->get_pm_sales();
$compSales = $sales->get_comp_sales();
$sales->disconnect();

Does the mysql connection close after the "connect" function executes? If deemed necessary, what would be the best way to keep the connection open (using an object oriented approach)? Please let me know if you need anymore details, and I appreciate the help in advance.

This is like totally unnecessary. You dont have to open and close connections for each query. Are you using some kind of a framework? If not you must as all frameworks have active records and DB helpers to make interacting with DB easier. THis would be a great article for you

http://net.tutsplus.com/tutorials/php/real-world-oop-with-php-and-mysql/

has just what youre lookng for.

In general, you only want to create your MySQL instance once during the execution of the application.

If you have an overarching Application object then you could just create your MySQL instance inside of the Application object and access it from there.

The other alternative is to create a Singleton object for your MySQL instance that is then accessed via an 'instance()' method.

This way you only open a single connection during the execution cycle of your php script and it will be discarded at the end of script execution.

So now your code looks like so:

$query = "SELECT * FROM users";

$rs = Mysql::instance()->query($query);

If you need working examples of how to setup a Singleton instance for your purposes you can look at:

• GacelaPHP
• Kohana Database Class
• Zend DB Adapter