sql - 发生错误 : "Cannot call methods on nvarchar."

Question

我写了一个查询来查找与特定问题相关的答案，但在运行此代码时收到此错误。

Cannot call methods on nvarchar

 select Posts.Id as Answer, ParentId as question, User.DisplayName as Answerer 
 FROM  Posts
INNER JOIN Users    ON Posts.OwnerUserId = Users.Id
WHERE 
ParentId in (SELECT Posts.Id
FROM  Posts
INNER JOIN PostTags ON Posts.Id          = PostTags.PostId
INNER JOIN Tags     ON PostTags.TagId    = Tags.id
INNER JOIN Users    ON Posts.OwnerUserId = Users.id
INNER JOIN PostTypes ON Posts.PostTypeId = PostTypes.Id
WHERE Tags.TagName   in 
(select 
   num.TagName as Tag

 from

(select TagName
from
Tags, PostTags, Posts
where Tags.Id = PostTags.TagId and Posts.Id = PostId
and Posts.CreationDate < '2015-04-20'
and Posts.CreationDate > '2015-01-01'
group by TagName) as rate

INNER JOIN
(select TagName 
from Tags, PostTags, Posts
where Tags.Id = PostTags.TagId and Posts.Id = PostId
group by TagName
having count(PostId) > 8000)as num 
ON rate.TagName = num.TagName
)
  AND Posts.AnswerCount > 1
  AND Posts.AcceptedAnswerId is not null
  AND Posts.Score > 0
  AND Posts.PostTypeId  = 1                -- PostTypeId = 1 -> Question
  AND Posts.CommunityOwnedDate is null
  )
AND Posts.PostTypeId  = 2                -- -> Answers

我认为问题是 ParentId ，但我不明白有什么问题。

Answer 1

您有保留字 User在您的查询中:

select Posts.Id as Answer, ParentId as question, User.DisplayName as Answerer

您需要将其修改为 [User].DisplayName
以下是有关 SQL 中保留字的重要资源: https://www.drupal.org/node/141051