您可以使用以下方法获得第一个订单的时间：

select user_id, min(created_at) as min_ca
from t
group by user_id;

接下来，您可以使用以下公式获得第一个订单的价格：

select oi.*
from order_items oi join
     (select user_id, min(created_at) as min_ca
      from order_items oi
      group by user_id
     ) ooi
     on oi.user_id = ooi.user_id and oi.created_at = ooi.min_ca
where oi.price = 0.00;

然后你就可以用 join , in ，或 exists ;

select oi.*
from order_items oi join
     order_items oi1
     on oi.user_id = oi1.user_id join
     (select user_id, min(created_at) as min_ca
      from order_items oi
      group by user_id
     ) u1
     on oi1.user_id = u1.user_id and oi1.created_at = u1.min_ca
where oi1.price = 0.00;

你可以用 EXISTS 为了检查零价格的记录没有更早的记录 created_at :

SELECT COUNT(*), user_id
FROM Promo
WHERE user_id IN (
    -- Query below yields [user_id]s of users who got the promo
    -- that wasn't a result of a cancellation and re-activation
    SELECT user_id
    FROM Promo p
    WHERE p.price = 0 AND NOT EXISTS (
        -- Look for a record with the same user ID and an earlier date
        -- than p.created_at, which is the date of the promo with 0.00 price
        SELECT *
        FROM Promo pp
        WHERE pp.user_id=p.user_id AND pp.created_at < p.created_at
    )
)
GROUP BY user_id