或附近的PostgreSQL语法错误。

Question

我尝试创建postgresql查询，以便从不同的表中获取相同的数据，但是执行时出现错误。在mysql中，我做了类似的查询

> ERROR:  syntax error at or near "."
  LINE 4:                             `B`.`_id` AS `_id`
                                         ^
> Time: 0.02s

我的查询

SELECT * 
FROM 
(
  SELECT
      `B`.`_id` AS `_id`
  FROM ( 
      SELECT 
       `apdi`.`id` AS `_id`               
      FROM `application_person_document_image` AS `apdi`
      INNER JOIN `application_person_document` AS `apd` ON `apdi`.`id` = `apd`.`application_person_document_id`
      INNER JOIN `application_person` AS `ap` ON `ap`.`id` = `apd`.`application_person_id`
      INNER JOIN `application` AS `a` ON `a`.`id` = `ap`.`application_id`   
      WHERE
      `a`.`id` = 196733                            
  ) AS `B`
  GROUP BY `B`.`_id`

UNION

  SELECT
      `N`.`_id` AS `_id`                        
  FROM (
      SELECT
       `app`.`id` AS `_id`,
      FROM `application_person_photo` AS `app`
      INNER JOIN `application_person` AS `ap` ON `ap`.`id` = `app`.`application_person_id`
      INNER JOIN `application` AS `a` ON `a`.`id` = `ap`.`application_id`
      WHERE
      `a`.`id` = 196733                             
  ) AS `N`
  GROUP BY `N`.`_id`
) AS t          

怎么了？我查看了文档，使用了别名。