sqlite join 查询 iPad

Question

我有三张桌子

Personal_video
+------------------------------+ 
 |presonal_video_id | title | 
  ----------------------------
       1            |  test1| 
       2            |  test2| 
       3            |  test3| 
       4            |  test4| 

personal_video_tags
+------------------------------+ 
     |tag_id |       tag_title | 
  ----------------------------
       1            |  august| 
       2            |  2016  | 
       3            |  2015  | 
       4            |  2014  | 


personal_video_tag_mapping
+------------------------------+ 
     |tag_id |       presonal_video_id | 
  ----------------------------
       1            |  1  | 
       2            |  2  | 
       3            |  3  | 
       4            |  1  | 

现在我想编写一个查询，它将根据常见标签返回视频，例如如果用户选择标签“August”和“2014”，那么查询应该返回连接到两个标签的视频。

目前我的查询是

 SELECT presonal_video_id,title 
 FROM personal_video 
 WHERE presonal_video_id IN 
 (
    SELECT personal_video_id AS PID 
    FROM personal_video_tag_mapping 
    WHERE tag_id IN ("1","2")  AND privacy_level != 2   
    GROUP BY personal_video_id 
    HAVING COUNT( PID ) > 1 
 )

它给了我写结果，但是当有大数据时，它需要很长时间。谁能告诉我写这个查询的正确方法

提前谢谢你

Answer 1

试试这个查询：

SELECT t1.presonal_video_id, t1.title 
FROM personal_video AS t1
JOIN personal_video_tag_mapping AS t2 
    ON t1.presonal_video_id = t2.presonal_video_id
JOIN personal_video_tags AS t3
    ON t2.tag_id = t3.tag_id    
WHERE t3.tag_title IN ('august', '2014')
GROUP BY t1.presonal_video_id, t1.title 
HAVING COUNT(*) = 2