Question

我正在尝试使用UserInfo与他的所有朋友以及他朋友的所有帖子以及这些帖子上的所有相关内容检索UserId=10004。为此，我使用的是查询：

select *,
    (select * ,
        (select * ,
            (select * from PostLikes where PostId=UserPosts.PostId) as likes
        from UserPosts where UserId=FriendsRelation.PersonId1 or UserId=FriendsRelation.PersonId2) as posts
    from FriendsRelation where PersonId1=UserId or PersonId2=UserId) as friends
from UserInfo 
where UserId=10004

但是它返回时出现错误

当未使用EXISTS
引入子查询时，只能在选择列表中指定一个表达式

我该如何解决？

以下是我正在使用的表格：

CREATE TABLE [dbo].[UserInfo]
(
    [UserId] [bigint] IDENTITY(1,1) NOT NULL,
    [Username] [nvarchar](max) NULL,
    [Email] [nvarchar](max) NOT NULL,
    [UserPassword] [nvarchar](max) NOT NULL,
    [Name] [nvarchar](max) NULL,
    [Gender] [nchar](10) NOT NULL,
    [ContactNo] [bigint] NOT NULL,
    [DateOfBirth] [date] NOT NULL,
    [RelationshipStatus] [nchar](10) NULL,
    [InterestedIn] [nchar](10) NULL,
    [Address] [nvarchar](max) NULL,
    [Country] [nchar](10) NOT NULL,
    [FavouriteQuote] [nvarchar](max) NULL,
    [DisplayPhoto] [nvarchar](max) NULL,
    [Guid] [nvarchar](max) NOT NULL,
    [Status] [tinyint] NOT NULL CONSTRAINT [DF_UserInfo_Status]  DEFAULT ((1)),
    [CreatedDate] [datetime] NOT NULL,
    [LastLogIn] [datetime] NULL,

    CONSTRAINT [PK_UserInfo] 
    PRIMARY KEY CLUSTERED ([UserId] ASC)
         WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
               IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
               ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

UserPosts表：

CREATE TABLE [dbo].[UserPosts]
(
    [PostId] [bigint] IDENTITY(1,1) NOT NULL,
    [UserId] [bigint] NOT NULL,
    [PostText] [nvarchar](max) NULL,
    [PostPicture] [nvarchar](max) NULL,
    [Time] [time](7) NOT NULL,
    [Date] [date] NOT NULL,
    [LikeCount] [int] NULL CONSTRAINT [DF_UserPosts_LikeCount]  DEFAULT ((0)),

    CONSTRAINT [PK_UserPosts] 
    PRIMARY KEY CLUSTERED ([PostId] ASC)
         WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
               IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
               ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

ALTER TABLE [dbo].[UserPosts]  WITH CHECK 
  ADD CONSTRAINT [FK_UserPosts_UserInfo] 
  FOREIGN KEY([UserId]) REFERENCES [dbo].[UserInfo] ([UserId])
     ON DELETE CASCADE
GO

ALTER TABLE [dbo].[UserPosts] CHECK CONSTRAINT [FK_UserPosts_UserInfo]
GO

和PostLikes表：

CREATE TABLE [dbo].[PostLikes]
(
    [LikeId] [bigint] IDENTITY(1,1) NOT NULL,
    [PostId] [bigint] NOT NULL,
    [UserId] [bigint] NOT NULL,

    CONSTRAINT [PK_PostLike] 
    PRIMARY KEY CLUSTERED ([PostId] ASC, [UserId] ASC)
         WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
               IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
               ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[PostLikes]  WITH CHECK 
  ADD CONSTRAINT [FK_PostLikes_UserInfo] 
    FOREIGN KEY([UserId]) REFERENCES [dbo].[UserInfo] ([UserId])
GO

ALTER TABLE [dbo].[PostLikes] CHECK CONSTRAINT [FK_PostLikes_UserInfo]
GO

ALTER TABLE [dbo].[PostLikes]  WITH CHECK 
  ADD CONSTRAINT [FK_PostLikes_UserPosts] 
    FOREIGN KEY([PostId]) REFERENCES [dbo].[UserPosts] ([PostId])
       ON DELETE CASCADE
GO

ALTER TABLE [dbo].[PostLikes] CHECK CONSTRAINT [FK_PostLikes_UserPosts]
GO

Answer 1

与其他人的答案类似，但是使用左连接（如果用户没有朋友），以及一些连接逻辑的更改。

declare @userID int = 10004 --For easy swapping out if you want to query someone else
Select * from UserInfo a
left join FriendsRelation b
    on b.PersonID1 = @userID or b.PersonID2 = @userID --Faster than joining and then filtering, if you're only looking for one person at a time
left join UserPosts c
    on (c.UserID = b.PersonID1 or c.UserID = b.PersonID2) 
    and c.UserID <> @userID --returns only friends' posts, not user's posts, as specified in original question
left join postLikes d
    on d.PostID = c.PostID
where a.UserID = @userID

Answer 2

如前所述，您需要使用join而不是子查询。可能这个查询对你有用

select * 
from UserInfo
  inner join FriendsRelation 
    on UserInfo.UserId = FriendsRelation.PersonId1
  inner join UserPosts
    on FriendsRelation.PersonId1 = UserPosts.UserId
  left outer join PostLikes
    on UserPosts.PostId = PostLikes.PostId
where UserInfo.UserId=10004
union
select * 
from UserInfo
  inner join FriendsRelation 
    on UserInfo.UserId = FriendsRelation.PersonId2
  inner join UserPosts
    on FriendsRelation.PersonId2 = UserPosts.UserId
  left outer join PostLikes
    on UserPosts.PostId = PostLikes.PostId
where UserInfo.UserId=10004

Answer 3

您可以像这样使用JOINS：

select * 
from UserInfo
  inner join FriendsRelation on UserInfo.UserId = FriendsRelation.PersonId1 or UserInfo.UserId = FriendsRelation.PersonId2
  inner join UserPosts on FriendsRelation.PersonId1 = UserPosts.UserId
  inner join PostLikes on UserPosts.PostId = PostLikes.PostId
where UserInfo.UserId=10004

在sql中查询多层表

3 个答案: