Question

我有两张桌子：

[ product_to_category
---------------------
product_id
category_id


[ category
---------------------
category_id
parent_id

我需要使用category.parent_id为'39'来获取所有product_id。这就是我正在尝试的，但是当它至少有几百个时它会返回空白：

SELECT
product_id
FROM
product_to_category
WHERE
category_id IN (
SELECT parent_id FROM category WHERE parent_id = '39'
)

我在这里尝试做的是什么？

Answer 1

知道了：

SELECT product_id FROM product_to_category INNER JOIN 类别ON product_to_category.category_id = category.category_id AND category.parent_id = 39

Answer 2

试试这个：

SELECT product_id
FROM product_to_category p2c
   Join category c 
      On c.category_id = p2c.category_id
Where parent_id = '39'

您在查询中的错误是：

 SELECT product_id
 FROM product_to_category
 WHERE category_id IN 
     (SELECT category_id   -- THIS IS WHERE YOUR SQL WAS INCORRECT
      FROM category WHERE parent_id = '39')

Answer 3

select product_id from product_to_category as ptc
inner join category as c
    on ptc.category_id = c.parent_id
where c.parent_id = 39

使用WHERE x IN选择语句（SELECT ...）

3 个答案: