5

我有三个表：视频、视频类别和类别。

表格如下所示：

videos: video_id, title, etc...
videos_categories: video_id, category_id
categories: category_id, name, etc...

在我的应用程序中，我允许用户多选类别。当他们这样做时，我需要返回每个选定类别中的所有视频。

我最终得到了这个：

SELECT * FROM videos WHERE video_id IN (
    SELECT c1.video_id FROM videos_categories AS c1
    JOIN c2.videos_categories AS c2
    ON c1.video_id = c2.video_id
    WHERE c1.category_id = 1 AND c2.category_id = 2
)

但是对于我添加到多选的每个类别，我都必须在我的内部选择中添加一个连接：

SELECT * FROM videos WHERE video_id IN (
    SELECT c1.video_id FROM videos_categories AS c1
    JOIN videos_categories AS c2
    ON c1.video_id = c2.video_id
    JOIN videos_categories AS c3
    ON c2.video_id = c3.video_id
    WHERE c1.category_id = 1 AND c2.category_id = 2 AND c3.category_id = 3
)

我不禁觉得这是真正错误的方法，但我在试图看到正确的方法时被阻止了。

4

3 回答 3

6

如果这是主键：

 videos_categories: video_id, category_id

那么 GROUP BY 和 HAVING 应该可以工作，试试这个：

SELECT
    * 
    FROM videos 
    WHERE video_id IN (SELECT 
                           video_id
                           FROM videos_categories
                           WHERE category_id IN (1,2,3)
                           GROUP BY video_id
                           HAVING COUNT(video_id)=3
                      )
于 2009-05-21T21:00:01.610 回答
0

这是一个 FOR XML PATH 解决方案：

--Sample data
CREATE TABLE Video
    (
    VideoID int,
    VideoName varchar(50)
    )

CREATE TABLE Videos_Categories
    (
    VideoID int,
    CategoryID int
    )

INSERT  Video(VideoID, VideoName)
SELECT  1, 'Indiana Jones'
UNION ALL
SELECT  2, 'Star Trek'

INSERT Videos_Categories(VideoID, CategoryID)
SELECT 1, 1
UNION ALL
SELECT 1, 2
UNION ALL
SELECT 1, 3
UNION ALL
SELECT 2, 1
GO

--The query
;WITH   GroupedVideos
AS
(
SELECT  v.*,
        SUBSTRING(
                    (SELECT  (', ') + CAST(vc.CategoryID AS varchar(20))
                    FROM     Videos_Categories AS vc
                    WHERE    vc.VideoID = v.VideoID
                    AND      vc.CategoryID IN (1,2)
                    ORDER BY vc.CategoryID
                    FOR XML PATH('')), 3, 2000) AS CatList
FROM    Video AS v
)

SELECT  *
FROM    GroupedVideos
WHERE   CatList = '1, 2'

（忽略下面的所有内容 - 我误读了这个问题）

尝试

WHERE c1.category_id IN (1,2,3)

或者

...
FROM videos v
JOIN Vedeos_categories vc ON v.video_id = vc.video_id
WHERE vc.category_id IN (1,2,3)

根本不需要多个连接。

编辑：将解决方案放在上下文中（我意识到这并不明显）：

SELECT * 
FROM videos 
WHERE video_id IN 
(    SELECT c1.video_id 
FROM videos_categories AS c1
WHERE c1.category_id = IN (1,2,3))

或者

SELECT *
FROM videos v
JOIN Vedeos_categories vc ON v.video_id = vc.video_id
WHERE vc.category_id IN (1,2,3)
于 2009-05-21T20:44:33.857 回答
0

听起来类似于SQL 搜索包含多个条件的行

为避免必须为每个类别进行另一个联接（并因此更改查询的结构），您可以将类别放入临时表中，然后针对该表进行联接。

CREATE TEMPORARY TABLE query_categories(category_id int);
INSERT INTO query_categories(category_id) VALUES(1);
INSERT INTO query_categories(category_id) VALUES(2);
INSERT INTO query_categories(category_id) VALUES(3);

SELECT * FROM videos v WHERE video_id IN (
  SELECT video_id FROM video_categories vc JOIN query_categories q ON vc.category_id = qc.category_id
  GROUP BY video_id
  HAVING COUNT(*) = 3
)

当然，尽管这本身就很丑陋。您可能想跳过临时表并在子查询中说“category_id IN (...)”。

于 2009-05-21T21:02:21.717 回答