<"aaa"')
      ->exists();
 
    if ($exists) {
      echo 'name=aaa 存在';
    }
 
    //定义字段别名
    //注意真实的字段名写后面，别名写前面
    $data4 = (new Query())->select(['ids' => 'id', 'names' => 'name'])
      ->from('{{%user}}')
      ->where('1=1')
      ->all();
 
    //通过orderby排序，和limit限制条数
    $data5 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where('1=1')
      ->orderBy('id desc')
      ->limit(3)
      ->all();
 
    //多个and条件
    //参数是数组，一个key对应一个value，默认以and拼接
    $data6 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['id' => 3, 'name' => 'aaa'])
      ->one();
 
    //in条件
    $data7 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['id' => [4, 5, 6]])
      ->all();
 
    //或者如下方式
    $data7_2 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['in', 'id', [4, 5, 6]])
      ->all();
 
    //count统计
    $count = (new Query())->from('{{%user}}')->count();
    echo '总记录数: ', $count;
 
    //大于，大于等于，小于，小于等于where条件
    $data8 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['>=', 'id', 5])
      ->all();
 
    $data9 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['<=', 'id', 3])
      ->all();
 
    //like查询
    $data10 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['like', 'name', 'dd'])
      ->all();
 
    //between筛选和group by分组
    //查找出age在18到24之间的，并按sex分组
    $data11 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['between', 'age', 18, 24])
      ->groupBy('sex')
      ->all();
 
    //having筛选
    //按sex分组，然后统计人数大于3的
    $data12 = (new Query())->select(['sex', 'cnt' => 'count(*)'])
      ->from('{{%user}}')
      ->groupBy('sex')
      ->having('cnt > 3')
      ->all();
 
    //or逻辑条件
    //查找姓名为aaa或bbb的用户
    //之前where数组是以key=>value方式传递的，如果要表达复杂逻辑关系，
    //数组第一个元素必须声明是什么逻辑，and还是or
    //第二个元素表示逻辑左边
    //第三个元素表示逻辑右边
    $data13 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['or', ['name' => 'aaa'], ['name' => 'bbb']])
      ->all();
 
    //复杂的where条件
    //我这里只是作为演示
    //SELECT `id`, `name` FROM `tb_user` WHERE ((`name`='aaa') OR (`name`='bbb')) OR ((`name`='ccc') OR (`name`='ddd'))
    $data14 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where([
        'or',
        [
          'or',
          ['name' => 'aaa'],
          ['name' => 'bbb'],
        ],
        [
          'or',
          ['name' => 'ccc'],
          ['name' => 'ddd'],
        ],
      ])
      ->all();
 
    //and和or嵌套where条件
    //SELECT `id`, `name` FROM `tb_user` WHERE (`sex`=1) AND ((`name` LIKE '%aa%') OR (`name` LIKE '%bb%'))
    $data15 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where([
        'and',
        ['sex' => 1],
        [
          'or',
          ['like', 'name', 'aa'],
          ['like', 'name', 'bb'],
        ],
      ])
      ->all();
 
    //有些时候我们需要根据用户传递过来的参数追加where条件
    //追加and条件
    $query = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where('sex=1');
    //追加age大于18的条件
    $query->andWhere(['>', 'age', 18]);
    echo $query->createCommand()->getRawSql();
 
    //追加or条件
    $query2 = (new Query())->select(['id', 'name'])
      ->from('{{%user}}')
      ->where(['like', 'name', 'aa']);
    //追加name相似bb的条件
    $query2->orWhere(['like', 'name', 'bb']);
    echo $query2->createCommand()->getRawSql();
 
    //表别名和连接查询
    //SELECT `u`.`id`, `u`.`name`, `aa`.`item_name` FROM `tb_user` `u` LEFT JOIN `tb_auth_assignment` `aa` ON aa.user_id = u.id
    $data16 = (new Query())->select(['u.id', 'u.name', 'aa.item_name'])
      ->from(['u' => '{{%user}}'])
      ->leftJoin(['aa' => '{{%auth_assignment}}'], 'aa.user_id = u.id')
      ->all();
  }
}