使用Select語句，其中X IN（SELECT ...）

Question

我有兩個表：

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


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

我需要把所有的product_id與 '39' 的category.parent_id。這裏就是我想要的，但如果至少有幾百它返回空：

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

是什麼，我想在這裏做可能嗎？

Answer 1

明白了：

SELECT的product_id FROM product_to_category INNER JOIN 類別在 product_to_category.category_id = category.category_id AND category.parent_id = 39

Answer 2

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 

Answer 3

試試這個：

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

你在做什麼錯在你的查詢是：

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')