Detailed explanation of some simple PHP database connection examples_PHP tutorial

$con = mysql_connect("localhost","root","");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
mysql_close($con);
?>

$mysqli = new mysqli('localhost','root','','volunteer');
if (mysqli_connect_errno()){
die('Unable to connect!'). mysqli_connect_error();
}
?>

$db = new PDO('mysql:host=localhost;dbname=test', 'root', '');
try {
foreach ($db->query('select * from user') as $row){
  print_r($row);
 }
 $db = null;  //关闭数据库
} catch (PDOException $e) {
 echo $e->getMessage();
}
?>

//------------------------------------------------ ------------------------------------------
// ※Database() Constructor, database initial parameters
// ※Select()                                                                                                                                                 // ※GetRows()                                                                                                                                                                                                                                                                                                // ※Insert()                                                                                                                                                                                   // ※Update()                                                                                     // ※Delete()                                                                                                              // ※Halt()                                                                                                                                                                             can interrupt and display the error message */
//------------------------------------------------ ------------------------------------------
define("DATABASETYPE", "1"); //Define database type: 1 is MySql; 2 is SQL Server; 3 is Oracle; 4 is Odbc
define("SERVER", "localhost"); //Host name or IP address of the database server
define("DATABASE", "dbName"); //The name of the database to be connected
define("USER", "tableName"); //Username used to connect to the database
define("PASSWORD", "paswd"); //Password used to connect to the database

class Database {
var $dbLink; var $dbLink; //Connection handle
var $result; var $result; //query handle
var $insId; var $insId; //Insert() successfully returns the value of the AUTO_INCREMENT column

var $numRows; var $numRows; //return the number of data
var $dbHost, $dbUser, $userPassword, $database;
var $dbType = DATABASETYPE;
var $msgFlag = "yes"; //yes:show the Mysql message; no: die by show "Halted."

function Database($dbHost = SERVER, $dbUser = USER, $userPassword = PASSWORD, $database = DATABASE) {
switch ($this->dbType) {
case 1:
                     $this->dbLink = @mysql_pconnect($dbHost, $dbUser, $userPassword); // or die("Can't Connect to Remote Host!");

                 break;
case 2:
                 break;
}
        return true;
}

/* SQL:Select() returns false and has no result */

    function Select($table, $columns, $condition = 1) {
        $sql = "select $columns from $table where $condition ";
        $this->result = @mysql_query($sql, $this->dbLink);
        unset($this->rows);
        if ($this->result) {
            $i = 0;
            if (!($this->rows = array("$i" => @mysql_fetch_array($this->result))))
                return false;
            if (($this->numRows = @mysql_num_rows($this->result)) == 0)
                return false;
            while ($tempRows = @mysql_fetch_array($this->result)) {
                array_push($this->rows, $tempRows);
            }
        } else {
            $this->Halt($sql);
            return false;
        }
        return true;
    }

    /* SQL:GetRows() 返回查询的记录总数 */

    function GetRows($table, $condition = 1) {
        $sql = "select count(1) as count from $table where $condition";
        $this->result = @mysql_query($sql, $this->dbLink);
        if ($this->result) {
            $temp = @mysql_fetch_array($this->result);
            $this->numRows = $temp[count];
        } else {
            $this->Halt($sql);
            return false;
        }
        return $this->numRows;
    }

    /* SQL:Insert() */

    function Insert($table, $columns, $values) {
        $sql = "insert into $table ($columns) values ($values)";
        $this->result = @mysql_query($sql, $this->dbLink);
        if ($this->result)
            $this->insId = @mysql_insert_id($this->dbLink);
        else {
            $this->Halt($sql);
            return false;
        }
        return true;
    }

    /* SQL:Update() */

    function Update($table, $setings, $condition) {
        $sql = "update $table set $setings where $condition";
        $this->result = @mysql_query($sql, $this->dbLink);
        if ($this->result)
            $this->numRows = @mysql_affected_rows($this->result);
        else {
            $this->Halt($sql);
            return false;
        }
        return true;
    }

    /* SQL:Delete */

    function Delete($table, $condition) {
        $sql = "delete from $table where $condition";
        $this->result = @mysql_query($sql, $this->dbLink);
        if ($this->result)
            $this->numRows = @mysql_affected_rows($this->result);
        else {
            $this->Halt($sql);
            return false;
        }
        return true;
    }

    /* Halt():error message */

    function Halt($msg) {
        if ($this->msgFlag == "yes") {
            printf("Database Query Error: %s
n", $msg);
            printf("MySql Error: %s
n", mysql_error());
        }else
            echo ""; //自定一个出错提示文件
        return false;
    }
}

switch ($db->dbType) {
    case 1:
        @mysql_close();
        break;
    case 2:
        break;
}
$db = new Database();
?>