SQL如何從內連接獲取最大值行

Question

我的用例是這樣的。

1. 我有餐廳。
2. 一間餐廳有許多餐廳項目。
3. 每個餐廳項目都有一個評級值。

我想獲得餐廳以及該餐廳的最高評價項目。

我的偽查詢將是這樣的。

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

在餐廳表中。

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

在 RESTAURANT_ITEMS 表中

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

期望的輸出是

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

Answer 1

我想這就是你要找的。 嘗試並確認。 :)

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)

問題后的以下編輯部分也已更新

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)

希望這對你現在有幫助:)

Answer 2

• 您可以在派生表中獲得餐廳的最高評級值。
• 將其連接回主表以獲得所需的輸出

請嘗試以下操作：

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)