Add condition to sub select in query

问题

I have this query

SELECT DISTINCT
    u.email,
    (
        SELECT
            count(DISTINCT o.id)
        FROM
            orders o
            INNER JOIN cart_dates cd ON cd.order_id = o.id
        WHERE
            u.id = o.user_id
    ) as count
FROM
    users u

How can I get rows only when count is, for example, < 20?

回答1:

you can use group by and having clause.

select u.email
from users u
inner join orders o on o.user_Id = u.id
inner join card_dates cd on cd.order_id = o.id
group by u.email
having count(distinct o.id) < 20

来源：https://stackoverflow.com/questions/59709945/add-condition-to-sub-select-in-query