發生錯誤：“無法在nvarchar上調用方法。”

Question

我寫了一個查詢來查找與特定問題相關的答案，但是在運行此代碼時收到了此錯誤。

無法在nvarchar上調用方法

 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

我認為問題是ParentId ，但我不明白出了什么問題。

Answer 1

您的查詢中有一個保留字User ：

選擇Posts.Id作為Answer，ParentId作為問題，User.DisplayName作為Answerer

您需要將其修改為[User].DisplayName

這是SQL中保留字的一個很好的資源： https ： //www.drupal.org/node/141051