我正在编写一个查询，该查询将用于分页社交Feed的结果。这个概念是移动应用程序将请求N个项目，并提供一个我在@CutoffTime下面称为的开始日期时间。截止时间的目的是确定何时应启动分页窗口。我们使用时间戳而不是行偏移量的原因是，即使添加了新的社交内容，时间戳也会使我们在获取较旧的帖子时从一致的位置进行分页。
由于社交Feed可以来自您自己或您的朋友，因此我使用UNION来合并这两个组的结果。最初，我尝试了TheQuery_CTE不使用的逻辑UNION，这太慢了。
这是我所做的（包括相关的表架构）：
CREATE TABLE [Content].[Photo]
(
[PhotoId] INT NOT NULL PRIMARY KEY IDENTITY (1, 1),
[Key] UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID(),
[FullResolutionUrl] NVARCHAR(255) NOT NULL,
[Description] NVARCHAR(255) NULL,
[Created] DATETIME2(2) NOT NULL DEFAULT SYSUTCDATETIME(),
);
CREATE TABLE [Content].[UserPhotoAssociation]
(
[PhotoId] INT NOT NULL,
[UserId] INT NOT NULL,
[ShowInSocialFeed] BIT NOT NULL DEFAULT 0,
CONSTRAINT [PK_UserPhotos] PRIMARY KEY ([PhotoId], [UserId]),
CONSTRAINT [FK_UserPhotos_User] FOREIGN KEY ([UserId])
REFERENCES [User].[User]([UserId]),
CONSTRAINT [FK_UserPhotos_Photo] FOREIGN KEY ([PhotoId])
REFERENCES [Content].[Photo]([PhotoId])
);
CREATE TABLE [Content].[FlaggedPhoto]
(
[FlaggedPhotoId] INT NOT NULL PRIMARY KEY IDENTITY(1,1),
[PhotoId] INT NOT NULL,
[FlaggedBy] INT NOT NULL,
[FlaggedOn] DATETIME2(0) NOT NULL DEFAULT SYSDATETIME(),
[FlaggedStatus] INT NOT NULL DEFAULT 1,
[ReviewedBy] INT NULL,
[ReviewedAt] DATETIME2(0) NULL
CONSTRAINT [FK_Photos_PhotoId_to_FlaggedPhotos_PhotoId] FOREIGN KEY ([PhotoId])
REFERENCES [Content].[Photo]([PhotoId]),
CONSTRAINT [FK_FlaggedPhotoStatus_FlaggedPhotoStatusId_to_FlaggedPhotos_FlaggedStatus] FOREIGN KEY ([FlaggedStatus])
REFERENCES [Content].[FlaggedContentStatus]([FlaggedContentStatusId]),
CONSTRAINT [FK_User_UserId_to_FlaggedPhotos_FlaggedBy] FOREIGN KEY ([FlaggedBy])
REFERENCES [User].[User]([UserId]),
CONSTRAINT [FK_User_UserId_to_FlaggedPhotos_ReviewedBy] FOREIGN KEY ([ReviewedBy])
REFERENCES [User].[User]([UserId])
);
CREATE TABLE [User].[CurrentConnections]
(
[MonitoringId] INT NOT NULL PRIMARY KEY IDENTITY,
[Monitor] INT NOT NULL,
[Monitored] INT NOT NULL,
[ShowInSocialFeed] BIT NOT NULL DEFAULT 1,
CONSTRAINT [FK_Monitoring_Monitor_to_User_UserId] FOREIGN KEY ([Monitor])
REFERENCES [dbo].[User]([UserId]),
CONSTRAINT [FK_Monitoring_Monitored_to_User_UserId] FOREIGN KEY ([Monitored])
REFERENCES [dbo].[User]([UserId])
);
CREATE TABLE [Content].[PhotoLike]
(
[PhotoLikeId] INT NOT NULL PRIMARY KEY IDENTITY,
[PhotoId] INT NOT NULL,
[UserId] INT NOT NULL,
[Created] DATETIME2(2) NOT NULL DEFAULT SYSUTCDATETIME(),
[Archived] DATETIME2(2) NULL,
CONSTRAINT [FK_PhotoLike_PhotoId_to_Photo_PhotoId] FOREIGN KEY ([PhotoId])
REFERENCES [Content].[Photo]([PhotoId]),
CONSTRAINT [FK_PhotoLike_UserId_to_User_UserId] FOREIGN KEY ([UserId])
REFERENCES [User].[User]([UserId])
);
CREATE TABLE [Content].[Comment]
(
[CommentId] INT NOT NULL PRIMARY KEY IDENTITY,
[PhotoId] INT NOT NULL,
[UserId] INT NOT NULL,
[Comment] NVARCHAR(255) NOT NULL,
[Created] DATETIME2(2) NOT NULL DEFAULT SYSUTCDATETIME(),
[CommentOrder] DATETIME2(2) NOT NULL DEFAULT SYSUTCDATETIME(),
[Archived] DATETIME2(2) NULL,
CONSTRAINT [FK_Comment_PhotoId_to_Photo_PhotoId] FOREIGN KEY ([PhotoId])
REFERENCES [Content].[Photo]([PhotoId]),
CONSTRAINT [FK_Comment_UserId_to_User_UserId] FOREIGN KEY ([UserId])
REFERENCES [User].[User]([UserId])
);
/*
End table schema
*/
DECLARE @UserId INT,
@NumberOfItems INT,
@CutoffTime DATETIME2(2) = NULL -- Stored Proc input params
-- Make the joins and grab the social data we need once since they are used in subsequent queries that aren't shown
DECLARE @SocialFeed TABLE ([Key] UNIQUEIDENTIFIER, [PhotoId] INT
, [Description] NVARCHAR(255), [FullResolutionUrl] NVARCHAR(255)
, [Created] DATETIME2(2), [CreatorId] INT, [LikeCount] INT
, [CommentCount] INT, [UserLiked] BIT);
-- Offset might be different for each group
DECLARE @OffsetMine INT = 0, @OffsetTheirs INT = 0;
IF @CutoffTime IS NOT NULL
BEGIN
-- Get the offsets
;WITH [GetCounts_CTE] AS
(
SELECT
[P].[PhotoId] -- INT
, 1 AS [MyPhotos]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
[FP].[FlaggedStatus] = 3 -- Flagged photos that are confirmed apply to everyone
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
AND
[UPA].[UserId] = @UserId -- Show the requesting user
AND
[P].[Created] >= @CutoffTime -- Get the newer items
UNION
SELECT
[P].[PhotoId] -- INT
, 0 AS [MyPhotos]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
INNER JOIN [User].[CurrentConnections] [M] ON
[M].[Monitored] = [UPA].[UserId]
AND
[M].[Monitor] = @UserId AND [M].[ShowInSocialFeed] = 1 -- this join isn't present above
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
(
[FP].[FlaggedStatus] = 3
OR
([FP].[FlaggedBy] = @UserId AND [FP].[FlaggedStatus] = 1)
) -- Flagged photos that are confirmed apply to everyone, pending flags apply to the user
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
AND
[P].[Created] >= @CutoffTime -- Get the newer items
)
SELECT
@OffsetMine = SUM(CASE WHEN [MyPhotos] = 1 THEN 1 ELSE 0 END)
, @OffsetTheirs = SUM(CASE WHEN [MyPhotos] = 0 THEN 1 ELSE 0 END)
FROM [GetCounts_CTE]
END
-- Prevent absence of social data from throwing an error below.
SET @OffsetMine = ISNULL(@OffsetMine, 0);
SET @OffsetTheirs = ISNULL(@OffsetTheirs, 0);
-- Actually select the data I want
;WITH TheQuery_CTE AS
(
SELECT
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
, COUNT(DISTINCT [PL].[PhotoLikeId]) AS [LikeCount] -- Count distinct used due to common join key
, COUNT(DISTINCT [C].[CommentId]) AS [CommentCount]
, CAST(ISNULL(MAX(CASE WHEN [PL].[UserId] = @UserId THEN 1 END), 0) AS BIT) AS [UserLiked]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
LEFT JOIN [Content].[PhotoLike] [PL] ON
[PL].[PhotoId] = [P].[PhotoId]
AND
[PL].[Archived] IS NULL
LEFT JOIN [Content].[Comment] [C] ON
[C].[PhotoId] = [P].[PhotoId]
AND
[C].[Archived] IS NULL
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
[FP].[FlaggedStatus] = 3 -- Flagged photos that are confirmed apply to everyone
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
AND
[UPA].[UserId] = @UserId -- Show the requesting user
GROUP BY
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
ORDER BY
[P].[Created] DESC
, [P].[Key] -- Ensure consistent order in case of duplicate timestamps
OFFSET @OffsetMine ROWS FETCH NEXT @NumberOfItems ROWS ONLY
UNION
SELECT
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
, COUNT(DISTINCT [PL].[PhotoLikeId]) AS [LikeCount]
, COUNT(DISTINCT [C].[CommentId]) AS [CommentCount]
, CAST(ISNULL(MAX(CASE WHEN [PL].[UserId] = @UserId THEN 1 END), 0) AS BIT) AS [UserLiked]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
INNER JOIN [User].[CurrentConnections] [M] ON
[M].[Monitored] = [UPA].[UserId]
AND
[M].[Monitor] = @UserId AND [M].[ShowInSocialFeed] = 1
LEFT JOIN [Content].[PhotoLike] [PL] ON
[PL].[PhotoId] = [P].[PhotoId]
AND
[PL].[Archived] IS NULL
LEFT JOIN [Content].[Comment] [C] ON
[C].[PhotoId] = [P].[PhotoId]
AND
[C].[Archived] IS NULL
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
(
[FP].[FlaggedStatus] = 3
OR
([FP].[FlaggedBy] = @UserId AND [FP].[FlaggedStatus] = 1)
) -- Flagged photos that are confirmed apply to everyone, pending flags apply to the user
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
GROUP BY
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
ORDER BY
[P].[Created] DESC
, [P].[Key] -- Ensure consistant order in case of duplicate timestamps
OFFSET @OffsetTheirs ROWS FETCH NEXT @NumberOfItems ROWS ONLY
)
INSERT INTO @SocialFeed ([Key], [PhotoId], [Description], [FullResolutionUrl]
, [Created], [CreatorId], [LikeCount], [CommentCount], [UserLiked])
SELECT TOP (@NumberOfItems)
[Key]
, [PhotoId]
, [Description]
, [FullResolutionUrl]
, [Created]
, [UserId]
, [LikeCount]
, [CommentCount]
, [UserLiked]
FROM [TheQuery_CTE]
ORDER BY -- Order here so the top works properly
[Created] DESC
, [Key] -- Ensure consistent order in case of duplicate timestamps
-- Output the social feed
SELECT
[P].[Key]
, [P].[PhotoId]
, [P].[Description] AS [PhotoDescription]
, [P].[FullResolutionUrl]
, [P].[Created] AS [Posted]
, [P].[CreatorId]
, [LikeCount]
, [CommentCount]
, [UserLiked]
FROM @Photos [P]
-- Select other data needed to build the object tree in the application layer
我知道我可以摆脱中的UNION问题，GetCounts_CTE但我认为它不会真正解决我在下面看到的任何问题。
我看到一些潜在的问题：
- 那是很多重复的逻辑，所以我可能会让自己的生活更艰难。
- 如果在计算计数和选择数据之间发生插入，我将关闭。我认为这种情况不会经常发生，但是会导致奇怪/难以调试的错误。
- 通过上述设置，人们会发现所有更聪明/更有经验的问题。
编写此查询的最佳方法是什么？奖励积分指出，解决方案使我的生活更简单。
编辑：
我不想选择所有数据并让客户端懒惰地显示项目，因为我不想通过强迫人们下载他们永远看不到的项目来滥用他们的数据计划。诚然，在宏伟的计划中，数据可能不会那么大，但是便士堆积……。
编辑2：
我强烈怀疑这不是最佳解决方案，但这是我到目前为止提出的最佳解决方案。
将我的UNION查询移至VIEW类似Greg的建议可以很好地隐藏该逻辑，并在我的存储过程中给出更简洁的查询。该视图还抽象了联合的丑陋/复杂性，这很好，因为我在选择中两次使用了它。这是该视图的代码：
CREATE VIEW [Social].[EverFeed]
AS
SELECT
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
, COUNT(DISTINCT [PL].[PhotoLikeId]) AS [LikeCount] -- Distinct due to common join key
, COUNT(DISTINCT [C].[CommentId]) AS [CommentCount]
, CAST(ISNULL(
MAX(CASE WHEN [PL].[UserId] = [UPA].[UserId] THEN 1 END), 0) AS BIT) AS [UserLiked]
, NULL AS [Monitor]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
LEFT JOIN [Content].[PhotoLike] [PL] ON
[PL].[PhotoId] = [P].[PhotoId]
AND
[PL].[Archived] IS NULL
LEFT JOIN [Content].[Comment] [C] ON
[C].[PhotoId] = [P].[PhotoId]
AND
[C].[Archived] IS NULL
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
[FP].[FlaggedStatus] = 3 -- Flagged photos that are confirmed apply to everyone
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
GROUP BY
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
UNION
SELECT
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
, COUNT(DISTINCT [PL].[PhotoLikeId]) AS [LikeCount]
, COUNT(DISTINCT [C].[CommentId]) AS [CommentCount]
, CAST(ISNULL(
MAX(CASE WHEN [PL].[UserId] = [M].[Monitor] THEN 1 END), 0) AS BIT) AS [UserLiked]
, [M].[Monitor]
FROM [Content].[Photo] [P]
INNER JOIN [Content].[UserPhotoAssociation] [UPA] ON
[UPA].[PhotoId] = [P].[PhotoId]
AND
[UPA].[ShowInSocialFeed] = 1
INNER JOIN [User].[CurrentConnections] [M] ON
[M].[Monitored] = [UPA].[UserId]
AND
[M].[ShowInSocialFeed] = 1
LEFT JOIN [Content].[PhotoLike] [PL] ON
[PL].[PhotoId] = [P].[PhotoId]
AND
[PL].[Archived] IS NULL
LEFT JOIN [Content].[Comment] [C] ON
[C].[PhotoId] = [P].[PhotoId]
AND
[C].[Archived] IS NULL
LEFT JOIN [Content].[FlaggedPhoto] [FP] ON
[FP].[PhotoId] = [P].[PhotoId]
AND
(
[FP].[FlaggedStatus] = 3
OR
([FP].[FlaggedBy] = [M].[Monitor] AND [FP].[FlaggedStatus] = 1)
) -- Flagged photos that are confirmed (3) apply to everyone
-- , pending flags (1) apply to the user
WHERE
[FP].[FlaggedPhotoId] IS NULL -- Filter out flagged photos
GROUP BY
[P].[Key]
, [P].[PhotoId]
, [P].[Description]
, [P].[FullResolutionUrl]
, [P].[Created]
, [UPA].[UserId]
, [M].[Monitor]
使用该视图，我将查询简化为以下内容。请注意，我正在OFFSET使用子查询进行设置。
DECLARE @UserId INT, @NumberOfItems INT, @CutoffTime DATETIME2(2);
SELECT
[Key]
, [PhotoId]
, [Description]
, [FullResolutionUrl]
, [Created]
, [UserId]
, [LikeCount]
, [CommentCount]
, [UserLiked]
FROM [Social].[EverFeed] [EF]
WHERE
(
([EF].[UserId] = @UserId AND [EF].[Monitor] IS NULL)
OR
[EF].[Monitor] = @UserId
)
ORDER BY -- Order here so the top works properly
[Created] DESC
, [Key] -- Ensure consistant order in case of duplicate timestamps
OFFSET CASE WHEN @CutoffTime IS NULL THEN 0 ELSE
(
SELECT
COUNT([PhotoId])
FROM [Social].[EverFeed] [EF]
WHERE
(
([EF].[UserId] = @UserId AND [EF].[Monitor] IS NULL)
OR
[EF].[Monitor] = @UserId
)
AND
[EF].[Created] >= @CutoffTime -- Get the newer items
) END
ROWS FETCH NEXT @NumberOfItems ROWS ONLY
该视图很好地将UNION了过滤的复杂性与过滤的分离。 我认为该子句中的子查询OFFSET将使整个查询变为原子，从而避免了我担心的并发问题。
我在键入此代码时发现的一个问题是：在上面的代码中，如果具有相同创建日期的两张照片位于不同的“页面”上，则后续页面上的照片将被滤除。考虑以下数据：
PhotoId | Created | ...
------------------------
1 | 2015-08-26 01:00.00
2 | 2015-08-26 01:00.00
3 | 2015-08-26 01:00.00
在初始页面上页面大小为1的PhotoId 1将被返回。如果第二页上的页面大小相同，则不会返回任何结果。我想为了解决这个问题，我将不得不添加KeyGuid作为参数...。