Database | MySql | PDO and Basic Connection

# MySqli - OOP version Connection and PHP Scrip--------(mysqli)------------
$host = "localhost";
$username = "root";
$password = "";
$database = "";
$conn = new mysqli($host, $username, $password, $database);
$sql = 'SELECT * FROM employee';
$result = $conn->query($sql);
if ($result->num_rows > 0) {
  while($row = $result->fetch_assoc()) {
    var_dump($row);
  }
} else {
  echo "0 results";
}
$conn->close();
// mySQLi One line
$gptapi = $conn->query("SELECT description FROM gptapi WHERE id=52")->fetch_assoc()['description'];

// In One line result
$rate = mysql_fetch_array(mysql_query("SELECT rate FROM userPermission WHERE userid='3339'" , $conexion))['rate'];
$result = mysql_query("SELECT * FROM table1", $conexion);
$num_rows = mysql_num_rows($result);
// Query Chaining Fetching from 3 table
SELECT * FROM userPermission WHERE userid=(SELECT clave FROM usuario WHERE email=(SELECT salesPerson FROM tracking_Payment WHERE userid=11155));

# PDO Version ###########  Connection and PHP Script-----------------------
try {
    $pdoCon = new PDO( "mysql:host={$host}; dbname={$database}", $username, $password );
}
// show error
catch( PDOException $exception ){
    echo "Connection error: " . $exception->getMessage();
}

# Simple Query execute
$sql = "SELECT * FROM students ORDER BY id DESC";
$result = $pdoCon->prepare($sql); // PDO Connection Object
$result->execute();
$catalog = $result->fetchAll();
      
# Only field value
$sql= "SELECT image, personid FROM orders WHERE id=:id";
$result = $pdoCon->prepare($sql);
$result->bindParam(':id', $OrderID);
$result->execute();
$Order = $result->fetch(PDO::FETCH_ASSOC);
$OrderImage = $Order['image'];
  
# Update Value
$sql = "UPDATE users SET valuesetbyuser = $rate where username='$userName'";
$result = $pdoCon->prepare($sql);
$result->execute();

# Insert Data
$query = "INSERT INTO students SET name=:name, email=:email, age=:age, sex=:sex, hobby=:hobby, address=:address, image=:image, created=:created";

# prepare query for execution
$stmt = $pdoCon->prepare($query);

# bind the parameters
$stmt->bindParam(':name', $name);
$stmt->bindParam(':email', $email);
$stmt->bindParam(':age', $age);
$stmt->bindParam(':sex', $sex);
$stmt->bindParam(':hobby', $hobby);
$stmt->bindParam(':address', $address);
$stmt->bindParam(':image', $fileName);
// specify when this record was inserted to the database
$created=date('Y-m-d H:i:s');
$stmt->bindParam(':created', $created);

# Execute the query
if( $stmt->execute() ) {
    $lastInsertId = $pdoCon->lastInsertId();
    echo "<div class='alert alert-success'>Record was saved. <a href='details.php?id=". $lastInsertId ."'>View Record</a></div>";
} else {
    echo "<div class='alert alert-danger'>Unable to save record.</div>";
}



# Mysql version ### Update version might not working-------(mysql)-Update version might not working------------
$conn = mysql_connect($host, $username, $password);
if(! $conn ) {
	die('Could not connect: ' . mysql_error());
 } else {
    echo "connected Succefully";
 }
 mysql_select_db($database);
 $sql = 'SELECT * FROM employee';
 $result = mysql_query( $sql, $conn ); // Esecute the query
 
 while($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
     var_dump($row);
 }
mysql_close($conn);

# Insert or Update | Count rows
$sql = "SELECT * FROM calenderapi WHERE userid=$userId";
$result = mysql_query($sql, $conexion);
$num_rows = mysql_num_rows($result);
if($num_rows<=0) {
$sql = "INSERT";
} else {
$sql = "UPDATE";
}