SQL查詢重複

Question

我的查詢是這樣設置（不能正常工作）

SELECT RentACar.dbo.Car.car_id as clm_CAR_ID, 
RentACar.dbo.Car_Image.car_image_url as clm_PICTURE_URL, 
RentACar.dbo.Users.user_agent_name as clm_USERNAME 

from RentACar.dbo.Car 

left join RentACar.dbo.Users 
on RentACar.dbo.Car.car_user_id = RentACar.dbo.Users.user_id 

left join RentACar.dbo.Car_Image 
on RentACar.dbo.Car.car_id = RentACar.dbo.Car_Image.car_image_car_id 

我的目標是，在顯示所有car_table汽車蒙山的USER_TABLE user_name和 picture_url image_table的。

但在image_table我有一個問題.. 一輛車可以有多個圖片。

---

此查詢結果;

clm_CAR_ID  clm_PICTURE_URL         clm_USERNAME   
1  NULL           ac ad 
2  NULL           ac ad 
3  NULL           ac ad 
4  NULL           ac ad 
5  /upload/10CeskUntitled23-11.png         ac ad 
5  /upload/10CveloperDesktopdeskUntitl4ed-11.png       ac ad 
6  NULL           ac ad 
7  NULL           ac ad 
8  NULL           ac ad 
9  /upload/9ngsdeveloperDesktopmelekkım.jpg         ac ad 
9  /upload/9eskt1opmelekkktc.jpg         ac ad 
10  /upload/10CeveloperDesktopd2eskxm.jpg         ac ad 
10  /upload/10ngsdeveloperDesktopdeskxm.jpg         ac ad 
10  /upload/10sdeveloperDesktopdeskU5ntitled-11.png       ac ad 

---

但我expaction結果

clm_CAR_ID  clm_PICTURE_URL         clm_USERNAME   
1  NULL           ac ad 
2  NULL           ac ad 
3  NULL           ac ad 
4  NULL           ac ad 
5  /upload/10CeskUntitled23-11.png         ac ad 
6  NULL           ac ad 
7  NULL           ac ad 
8  NULL           ac ad 
9  /upload/9ngsdeveloperDesktopmelekkım.jpg         ac ad 
10  /upload/10CeveloperDesktopd2eskxm.jpg         ac ad 

Answer 1

既然你沒有指定哪個RDBMS您使用我張貼的最通用的答案我可以想出：

SELECT Car_ID AS clm_CAR_ID, 
     Car_Image_URL AS clm_PICTURE_URL, 
     user_agent_name AS clm_USERNAME 
FROM Car 
     INNER JOIN Users 
      ON Car_User_ID = User_ID 
     LEFT JOIN 
     ( SELECT Img.* 
      FROM Car_Image Img 
        INNER JOIN 
        ( SELECT MIN(Image_ID) AS Image_ID 
         FROM Car_Image 
         GROUP BY Car_Image_Car_ID 
        ) AS MaxImg 
         ON MaxImg.Image_ID = Img.Image_ID 
     ) AS Img 
      ON Img.Car_Image_Car_ID = Car_ID; 

我已經在This SQL Fiddle上測試過它，它適用於MySQL，MSSQL，PostgreSQL和SQLLite。我幾乎沒有使用Oracle的經驗，因此無法在使用Oracle進行測試時修復語法錯誤。

Answer 2

你應該加入Car_Table，USER_TABLE。
然後加入Image_Table，其中 包含每輛車一張照片。

SELECT car_id, user_name, image_url 
FROM 
    (Car_Table JOIN User_Table AS cars_and_photos ON car_user_id = user_id) JOIN 
    (SELECT * FROM Image_Table GROUP_BY image_car_id) AS one_photo_per_car 
ON one_photo_per_car.image_car_id = cars_and_photos.user_id 

我沒有測試此查詢

Answer 3

SELECT rentacar.dbo.car.car_id, 
     rentacar.dbo.car_image.car_image_url AS image, 
     rentacar.dbo.users.user_agent_name AS USER 
from rentacar.dbo.car 
left join rentacar.dbo.car_image 
on rentacar.dbo.car.car_id = rentacar.dbo.car_image.image_car_id 
left join rentacar.dbo.users 
on rentacar.dbo.car.car_user_id = rentacar.dbo.users.user_id