mysqli使用封装举例

class mysqliClass
{
    private $DB_HOST = 'localhost';
    private $DB_NAME = 'demo_db';
    private $DB_USER = 'root';
    private $DB_PWD  = 'root';
    private $DB_PORT = 3306;

    protected $con = '';

    /**
     * 构造函数，实例化MYSQL连接
     */
    function __construct()
    {
        $this->con = mysqli_connect($this->DB_HOST, $this->DB_USER, $this->DB_PWD, $this->DB_NAME, $this->DB_PORT);
    }

    /**
     * 获取一行数据
     * @param $sql
     * @return array|null
     */
    public function find($sql)
    {
        $result = mysqli_query($this->con, $sql);
        if ($result) {
            $re = mysqli_fetch_array($result, MYSQLI_ASSOC);
            mysqli_free_result($result);
            
            return $re;
        }
    }

    /**
     * 获取多行数据
     * @param $sql
     * @return array
     */
    public function select($sql)
    {
        $result = mysqli_query($this->con, $sql);
        if ($result) {
            $re = array();
            while ($row = mysqli_fetch_assoc($result))
            {
                $re[] = $row;
            }
            
            return $re;
        }
    }

    /**
     * 获取唯一数据
     * @param $sql
     * @return mixed
     */
    public function field($sql)
    {
        $result = mysqli_query($this->con, $sql);
        if ($result) {
            $row = mysqli_fetch_row($result);
            mysqli_free_result($result);

            if (isset($row[0])) {
                return $row[0];
            }
        }
    }

    /**
     * 执行命令
     * @param $sql
     * @return mixed
     */
    public function query($sql)
    {
        if (mysqli_query($this->con, $sql)) {
            return mysqli_affected_rows($this->con);
        }
    }
}