A very simple example how to use mysqli

class.database.php

<?php

/**
 * Class Database using mysqli
 *
 * @link https://gist.github.com/ceceprawiro/4f8072ffa3ee412f2f13
 * @author Cecep Prawiro
 */
class Database
{
    private $db;
    public $result;

    /**
     * Connect to MySQL server and change database.
     *
     * @param String $db_hostname
     * @param String $db_username
     * @param String $db_password
     * @param String $db_database
     *
     * @return void
     */
    public function __construct($db_hostname, $db_username, $db_password, $db_database)
    {
        /* Trying to connect to database */
        $this->db = @new mysqli($db_hostname, $db_username, $db_password, $db_database);
        if ($this->db->connect_errno) trigger_error('Database Error ('.$this->db->connect_errno.'): ' . $this->db->connect_error, E_USER_ERROR);

        /* Trying to use database */
        if ($this->db->select_db($db_database) === false) trigger_error('Database Error ('.$this->db->errno.'): ' . $this->db->error, E_USER_ERROR);
    }

    /**
     * Performs a query on the database.
     *
     * @param String $sql The query string.
     *                    Example:
     *                      SELECT * FROM posts WHERE id = '%i'
     *                      SELECT * FROM posts WHERE title LIKE '%%s%'
     *                    Note:
     *                      i = integer
     *                      d = double
     *                      s = string
     *                      b = blob
     * @param Array  $args Variables for the parameter markers in the SQL statement.
     * @return stdObject Object.
     */
    public function query($sql, $parameters = [])
    {
        if (! is_array($parameters)) $parameters = [$parameters];

        $stmt = $this->prepare($sql, $parameters);
        $stmt->execute();

        $stmt->store_result();
        $this->result = (object) [
            'affected_rows' => $stmt->affected_rows,
            'insert_id'     => $stmt->insert_id,
            'num_rows'      => $stmt->num_rows,
            'field_count'   => $stmt->field_count,
            'errno'         => $stmt->errno,
            'error'         => $stmt->error,
            'records'       => $stmt->num_rows > 0 ? $this->fetch($stmt) : null,
        ];
        $stmt->close();

        return $this->result;
    }

    /**
     * Prepare statement and bind parameters.
     *
     * @param string $sql        The query string.
     * @param array  $parameters Variables to passed to mysqli_prepare.
     * @return mysqli_stmt Object.
     */
    private function prepare($sql, $parameters)
    {
        // Example query:
        // "SELECT * FROM table WHERE id = %i"
        $map = array(
            '%i' => 'i', //integer
            '%d' => 'd', //float
            '%s' => 's', //string
        );
        $pattern = '/(' . implode('|', array_keys($map)) . ')/';

        if (preg_match_all($pattern, $sql, $matches)) {
            $types = implode('', $matches[0]);
            $types = strtr($types, $map);

            /* Prepare statement */
            $sql = preg_replace($pattern, '?', $sql);

            $stmt = $this->db->prepare($sql);
            if ($stmt === false) trigger_error('SQL Error ('.$this->db->errno.'): ' . $this->db->error, E_USER_ERROR);

            /*
            mysqli_stmt_bind_param() requires parameters to be passed by
            reference, whereas in PHP 5.3+ call_user_func_array() can accept as
            a parameter a list of variables that can represent references or
            values.

            Also see fetch() method.
            */
            array_unshift($parameters, $types);
            foreach ($parameters as $key => $value) {
                $parameters[$key] = &$parameters[$key];
            }

            call_user_func_array([$stmt, 'bind_param'], $parameters);
        } else {
            /* Prepare statement */
            $stmt = $this->db->prepare($sql);
        }

        return $stmt;
    }

    /**
     * Gets a result set from a prepared statement.
     *
     * @param mysqli_stmt Object $stmt The mysqli statement object.
     * @return array.
     */
    private function fetch($stmt)
    {
        $meta = $stmt->result_metadata();

        while ($field = $meta->fetch_field()) {
            $params[] = &$row[$field->name];
        }

        call_user_func_array([$stmt, 'bind_result'], $params);

        $result = null;
        while ($stmt->fetch()) {
            foreach($row as $key => $val) {
                $field[$key] = $val;
            }
            $result[] = $field;
        }

        return $result;
    }
}

/*
 Let's create an example!
 Here we want to extends the Database Class.

 DROP TABLE IF EXISTS user;
 CREATE TABLE IF NOT EXISTS user (
    id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
    username VARCHAR(100) NOT NULL DEFAULT '',
    password VARCHAR(65) NOT NULL DEFAULT '',
    PRIMARY KEY (id),
    UNIQUE (username)
 );

 INSERT INTO user (username, password) VALUES
 ('Dian',    SHA2('dian',    0)),
 ('Sastro',  SHA2('sastro',  0)),
 ('Wardoyo', SHA2('wardoyo', 0));
 */

define('DB_HOSTNAME', 'localhost');
define('DB_USERNAME', 'root');
define('DB_PASSWORD', 'root');
define('DB_DATABASE', 'test');

class UsersModel extends Database
{
    /**
     * The constructor.
     */
    public function __construct()
    {
        parent::__construct(DB_HOSTNAME, DB_USERNAME, DB_PASSWORD, DB_DATABASE);
    }

    public function get_all()
    {
        return $this->query('SELECT * FROM user');
    }

    public function get_by_id($id)
    {
        return $this->query('SELECT * FROM user WHERE id = %i', [$id]);
    }

    public function get_by_username($username)
    {
        // Be careful when using % with LIKE.
        return $this->query("SELECT * FROM user WHERE username LIKE %%s%", [$username]);
    }

    public function insert($values)
    {
        return $this->query('INSERT INTO user (username, password) VALUES (%s, %s)', $values);
    }

    public function update($id, $values)
    {
        array_unshift($values, $id);
        return $this->query('UPDATE user SET username = %s, password = %s WHERE id = %i', $values);
    }

    public function delete($id)
    {
        return $this->query('DELETE FROM user WHERE id = %i', [$id]);
    }
}

$users = new UsersModel();
$result = $users->insert(['Raisa', hash('sha256', 'raisa')]);
$result = $users->insert(['Andriana', hash('sha256', 'andriana')]);
$result = $users->get_all();
foreach ($result->records as $user)
    printf('id = %1$d, username = %2$s, password = %3$s<br/>', $user['id'], $user['username'], $user['password']);

// Duplicate entry 'Raisa'
$result = $users->insert(['Raisa', hash('sha256', 'raisa')]);
echo '<pre>'; print_r($result); echo '</pre>';

// Get all records after duplicate entry
$result = $users->get_all();
foreach ($result->records as $user)
    printf('id = %1$d, username = %2$s, password = %3$s<br/>', $user['id'], $user['username'], $user['password']);