今天写一个小的应用场景，不多废话，直接上代码。

<?php
/**
 * Created by ZhengNiu.
 * User: 77103
 * Date: 2019/4/4
 * Time: 15:19
 */

namespace app\helper;

class db
{
  private $sql = [
      'table' => '',
      'field' => '*',
      'where' => '',
      'order' => '',
      'limit' => ''
  ];
  protected $where = '';
  protected $order = '';
  protected $limit = '';

  public function __call($name, $arguments)
  {
      if (array_key_exists($name, $this->sql)) {
          $this->sql[$name] = $arguments[0];
      }
      return $this;
  }

  public function select()
  {
      if (!empty($this->sql['where'])) {
          $this->where = ' where ' . $this->sql['where'];
      }
      if (!empty($this->sql['order'])) {
          $this->order = ' order by ' . $this->sql['order'];
      }
      if (!empty($this->sql['limit'])) {
          $this->limit = ' limit ' . $this->sql['limit'];
      }
      $sql = 'select ' . $this->sql['field'] . ' from ' . $this->sql['table'] . $this->where . $this->order . $this->limit;
      echo $sql;
  }
}
// 调用
$db = new db();
$db->table('user')->field('id,username,email,age')->where("email like '%qq.com%'")->order('id desc')->limit('1,10')->select();
Logic::vd($db);