SQL如何从内连接获取最大值行

Question

我的用例是这样的。

1. 我有餐厅。
2. 一间餐厅有许多餐厅项目。
3. 每个餐厅项目都有一个评级值。

我想获得餐厅以及该餐厅的最高评价项目。

我的伪查询将是这样的。

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

在餐厅表中。

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

期望的输出是

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

Answer 1

我想这就是你要找的。 尝试并确认。 :)

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)

问题后的以下编辑部分也已更新

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)

希望这对你现在有帮助:)

Answer 2

• 您可以在派生表中获得餐厅的最高评级值。
• 将其连接回主表以获得所需的输出

请尝试以下操作：

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)