SQL 查询 : count for all the reviews that each customer has written

Question

假设我有一个名为“REVIEWS”的表

此表包含客户为各种产品撰写的评论。

我希望能够对每个客户撰写的所有评论进行“计数”， 所以我写:

SELECT count(*) AS counter
FROM reviews 
WHERE customers_id = 12345

现在，我的问题是我希望有一个像上面那样的计数，但只针对写了特定产品评论的客户

例如，

SELECT customers_review
FROM reviews
WHERE
products_id = '170' 

总而言之，我希望能够获得客户撰写的每条评论的总计数，但仅限于为特定产品撰写评论的客户。

Answer 1

select customers_id, count(*)
from reviews
where customers_id in 
(select customers_id from reviews where products_id = '170')
group by customers_id;