进行一个查询以连接多个表

Question

我有3张桌子：

1. 营养表，它是具有所有营养nutrition_id和nutrition_name
的静态表
2. 包含产品信息且列为product_id，product_name，brand
的产品表
3. product_nutritions这是一个中间人表，它将产品与营养成分及其价值联系起来。结构为product_id，nutrition_id，nutrition_value。每种产品可以有1行或更多，具体取决于它具有的营养成分的数量。

这是一个真实的测试示例

营养表

nutrition_id |nutrition_name
           1 | caloreis    
           2 | fat    
           3 | sugar    
           4 | salt

产品表

product_id| product_name           | brand   
        1 | Nutella Hazelnut Cocoa | Nutella    
        2 | Nutella Jar            | Nutella

product_nutrition table

product_id | nutrition_id | nutrition_value
         1 |            1 |             200
         1 |            2 |              15
         1 |            3 |               2
         1 |            4 |              11
         2 |            1 |             200
         2 |            2 |              15
         2 |            3 |              12
         2 |            4 |              11

但我需要创建一个查询，返回产品名称以及属于特定品牌的营养成分，其中糖的价值小于5.

以下是我尝试的查询

 SELECT * 
 FROM products pi
 INNER JOIN product_nutrition_facts pn ON pi.product_id = pn.product_id
 WHERE pn.nutrition_id
 IN (
 '2,4,1'
 )
 OR (
  pn.nutrition_value <=5
  AND pn.nutrition_id =3
 )
 HAVING p.brand ='Nutella'
 ORDER BY `pn`.`nutrition_id` DESC 
 LIMIT 0 , 10

该代码返回营养成分标签中甚至没有糖的产品！

有人可以帮忙吗？

Answer 1

试试这个：

SELECT 
    p.brand,
    p.product_name,
    n.nutrition_name,
    pn.nutrition_value
FROM
    product_nutritions pn,
    Products p,
    Nutritions n
WHERE
    pn.nutrition_id = n.nutrition_id
        AND pn.product_id = p.product_id
        AND p.brand = 'Nutella'
        AND n.nutrition_name = 'sugar'
        AND pn.nutrition_value <= 5;

编辑：试试这个： SELECT p.brand, p.product_name, n.nutrition_name, pn.nutrition_value FROM product_nutritions pn, Products p, Nutritions n WHERE pn.nutrition_id = n.nutrition_id AND pn.product_id = p.product_id AND p.id IN ( SELECT p.id FROM product_nutritions pn, Products p, Nutritions n WHERE pn.nutrition_id = n.nutrition_id AND pn.product_id = p.product_id AND p.brand = 'Nutella' AND n.nutrition_name = 'sugar' AND pn.nutrition_value <= 5 );

对于多种营养素，您可以这样做： SELECT p.brand, p.product_name, n.nutrition_name, pn.nutrition_value FROM product_nutritions pn, Products p, Nutritions n WHERE pn.nutrition_id = n.nutrition_id AND pn.product_id = p.product_id AND p.id IN ( SELECT p.id FROM product_nutritions pn, Products p, Nutritions n WHERE pn.nutrition_id = n.nutrition_id AND pn.product_id = p.product_id AND ( ( p.brand = 'Nutella' AND n.nutrition_name = 'sugar' AND pn.nutrition_value <= 5 ) OR ( p.brand = 'Nutella' AND n.nutrition_name = 'whatever' AND pn.nutrition_value <= whatevernumber ) );

`

Answer 2

我不是sql专家，但我认为这应该有所帮助。 https://support.sas.com/documentation/cdl/en/sqlproc/62086/HTML/default/viewer.htm#a001361784.htm。

Answer 3

使用JOIN声明

SELECT products.name as productName, nutrition.nutrition_name as NutritionName, product_nutrition.nutrition_value 
FROM product_nutrition 
INNER JOIN products on products.id = product_nutrition.product_id 
INNER JOIN Nutritions on Nutritions.id=product_nutrition.nutrition_id 
WHERE product_nutrition.nutrition_value = 'any value you want'