SQL如何从内连接获取最大值行

Question

My use case is something like this.

1. I have restaurants.
2. One restaurants has many restaurant items.
3. Each restaurant item has a rating value.

I want to get restaurants along with the top rated item for that restaurant.

I pseudo query will be something like this.

SELECT * FROM RESTAURANTS 
WHERE RESTAURANT_IDS = 1,2,3,4,5 
LEFT JOIN RESTAURANT_ITEMS 
WHERE ratings = MAX(ratings)

in RESTAURANTS table.

id|name
-------------
1 |McDonalds
2 |Pizzahut
3 |Buger king
4 |KFC

in RESTAURANT_ITEMS table

id|name      |rating| FK_RES_ID
----------------------------
1 |Pizza     |5     |2
2 |Lava cake |4     |2
3 |Veg burger|3     |4
4 |Chicken b |5.6   |4
5 |Ice cream |4.3   |1
6 |Burger    |5     |1

Desired output would be

id|name      |top item
----------------------
1 |McDonalds |Burger
2 |Pizzahut  |Pizza
3 |Buger king|Null
4 |KFC       |Chicken b

Answer 1

I suppose this is what you are looking for. Try and confirm. :)

SELECT 
      res.ResName
      ,item.Name as ResItem
      ,(Select max(SubItem.rating) from RESTAURANT_ITEMS SubItem where res.RestaurantID= SubItem.RestaurantID) as Rating
FROM 
      RESTAURANTS res
LEFT JOIN 
      RESTAURANT_ITEMS item on res.RestaurantID = item.RestaurantID
WHERE 
      res.Restaurant_ID in (1,2,3,4,5)

EDITED PART BELOW AFTER QUESTION WAS ALSO UPDATED

SELECT 
      res.Name as [Restaurant Name]
      ,item.Name as [Top Item]
FROM 
      RESTAURANTS res
LEFT JOIN 
      RESTAURANT_ITEMS item on res.RestaurantID = item.RestaurantID 
                            and rating = (select max(subItems.rating) from RESTAURANT_ITEMS subItems where subItems.RestaurantID = res.RestaurantID)
WHERE 
      res.Restaurant_ID in (1,2,3,4,5)

Hope this helps you now :)

Answer 2

• You can get the highest rating value in a Derived Table, for a Restaurant.
• Join it back to main tables to get the desired output

Try the following:

SELECT r.id, 
       r.name, 
       ri.name AS top_item 
FROM RESTAURANTS AS r 
LEFT JOIN (SELECT FK_RES_ID, MAX(rating) AS max_rating 
           FROM RESTAURANT_ITEMS 
           GROUP BY FK_RES_ID) AS dt 
  ON dt.FK_RES_ID = r.id 
LEFT JOIN RESTAURANT_ITEMS AS ri ON ri.FK_RES_ID = dt.FK_RES_ID AND 
                                    ri.rating = dt.max_rating 

WHERE r.id IN (1,2,3,4)