Question

我有3张桌子

分类

category_id int(11) auto increment PK
name varchar(100)

产品

category_id int(11) FK from increment 
product_id int(11) auto increment PK
Name varchar(100)

favourite_id int(11) auto increment PK
product_id int(11) FK from product
user_id int(11) FK from user

我想要数据所有产品name, category name, favourite = 1如果记录存在于收藏表中，则其他0为特定用户

Answer 1

您可以尝试类似

的内容

SELECT p.`name` , c.name AS categoryName  , IFNULL(f.user_id,0), IFNULL(f.product_id ,0)
FROM Category c INNER JOIN Product p 
ON c.category_id  = p.category_id 
LEFT JOIN Favourite f 
ON f.product_id =p.product_id

Answer 2

只需使用LEFT JOIN：

SELECT A.Name Product_Name, B.Name Category_Name 
FROM Product A LEFT JOIN Category B
ON A.category_id=B.category_id
LEFT JOIN Favourite C
ON A.product_id=C.product_id
WHERE favourite_id=1;

Answer 3

尝试此操作，$user_id用于特定用户

SELECT p.Name as product_name, c.Name as Category_name 
FROM Product p 
JOIN Category c ON p.category_id=c.category_id
JOIN Favourite f ON p.product_id=f.product_id
WHERE f.user_id= '$user_id';

如果存在或不存在记录，如何从多个表中获取数据

3 个答案: