我有以下在 SQL Server CE 4 上运行的 SQL 查询
SELECT [Join_ReleaseMinDatePost].[FK_MovieID]
FROM (
SELECT [FK_MovieID], MIN([DatePost]) AS [ReleaseMinDatePost]
FROM [Release]
GROUP BY [FK_MovieID]
) [Join_ReleaseMinDatePost]
INNER JOIN
(
SELECT COUNT([ID]) AS [FolderCount], [FK_MovieID]
FROM [MovieFolder]
GROUP BY [FK_MovieID]
) [Join_MovieFolder]
ON [Join_MovieFolder].[FK_MovieID] = [Join_ReleaseMinDatePost].[FK_MovieID]
此查询需要很长时间才能执行,但如果我更改部分
SELECT COUNT([ID]) AS [FolderCount], [FK_MovieID] FROM [MovieFolder] GROUP BY [FK_MovieID]
到
SELECT 1 AS [FolderCount], [FK_MovieID] FROM [MovieFolder]
所以完整的查询变成
SELECT [Join_ReleaseMinDatePost].[FK_MovieID]
FROM ( SELECT [FK_MovieID], MIN([DatePost]) AS [ReleaseMinDatePost] FROM [Release] GROUP BY [FK_MovieID] ) [Join_ReleaseMinDatePost]
INNER JOIN (SELECT 1 AS [FolderCount], [FK_MovieID] FROM [MovieFolder] ) [Join_MovieFolder]
ON [Join_MovieFolder].[FK_MovieID] = [Join_ReleaseMinDatePost].[FK_MovieID]
然后性能变得非常快。
问题是,如果单独使用,则更改的部分非常快。但由于某种原因,第一个查询的执行计划显示索引扫描中的“实际行数”为 160,016,而表 MovieFolder 中的总行数为 2,192。并且“估计的行数”是 2,192。
所以我认为问题出在行数上,但我不知道为什么一切都搞砸了。
任何帮助将不胜感激:)谢谢
表的架构如下
CREATE TABLE [Release] (
[ID] int NOT NULL
, [FD_ForumID] int NOT NULL
, [FK_MovieID] int NULL
, [DatePost] datetime NULL
);
GO
ALTER TABLE [Release] ADD CONSTRAINT [PK__Release__0000000000000052] PRIMARY KEY ([ID]);
GO
CREATE INDEX [IX_Release_DatePost] ON [Release] ([DatePost] ASC);
GO
CREATE INDEX [IX_Release_FD_ForumID] ON [Release] ([FD_ForumID] ASC);
GO
CREATE INDEX [IX_Release_FK_MovieID] ON [Release] ([FK_MovieID] ASC);
GO
CREATE UNIQUE INDEX [UQ__Release__0000000000000057] ON [Release] ([ID] ASC);
GO
CREATE TABLE [MovieFolder] (
[ID] int NOT NULL IDENTITY (1,1)
, [Path] nvarchar(500) NOT NULL
, [FK_MovieID] int NULL
, [Seen] bit NULL
);
GO
ALTER TABLE [MovieFolder] ADD CONSTRAINT [PK_MovieFolder] PRIMARY KEY ([ID]);
GO
CREATE INDEX [IX_MovieFolder_FK_MovieID] ON [MovieFolder] ([FK_MovieID] ASC);
GO
CREATE INDEX [IX_MovieFolder_Seen] ON [MovieFolder] ([Seen] ASC);
GO
CREATE UNIQUE INDEX [UQ__MovieFolder__0000000000000019] ON [MovieFolder] ([ID] ASC);
GO
CREATE UNIQUE INDEX [UQ__MovieFolder__0000000000000020] ON [MovieFolder] ([Path] ASC);
GO