Question

我有两张桌子：

会话：此表包含用户拥有的所有会话。它包含3列。 uuid，user_id，happen_at

购买：此表包含用户所做的所有购买。它包含3列：purchase_id，user_id，buying_at

问题：对于每个会话，找到用户在会话时已经进行的购买数量

伪代码：

for session in sessions:
   current_session_user_id = session["user_id"]
   current_session_timestamp = session["occurred_at"]
   num_purchases_made_at_the_time = query(
      SELECT count(*) FROM purchases 
      WHERE
          purchases.user_id =  current_session_user_id
          AND purchases.purchased_at < current_session_timestamp
   )

注意：我的数据库（vertica）

不支持非相等相关子查询表达式

一些想法，因为我无法使用相关子查询：

编写一个CTE，为每个用户发生每个订单计数的索引，然后加入。（）

Answer 1

你的意思是CTE作为公共表格表达还是...... CTE作为条件真实事件？： - ）

如果你有：

SQL> select * from sessions order by uuid;
 uuid | user_id |     occurred_at     
------+---------+---------------------
    1 |     100 | 1959-03-07 04:31:15
    2 |     100 | 1969-03-07 05:31:15
    3 |     200 | 1979-03-07 06:31:15
    4 |     200 | 1989-03-07 07:31:15
    5 |     300 | 1999-03-07 08:31:15

和

SQL> select * from purchases order by purchase_id;
 purchase_id | user_id |    purchased_at     
-------------+---------+---------------------
        1000 |     100 | 1959-03-07 04:32:15
        1001 |     100 | 1959-03-07 04:33:15
        1002 |     100 | 1969-03-07 05:32:15
        1003 |     200 | 1979-03-07 06:32:15
        1004 |     300 | 1999-03-07 08:32:15

然后：

SQL> select max(a.user_id) as user_id, a.occurred_at, max(a.cte) as num_purchases 
     from ( select s.user_id, s.occurred_at,
                   conditional_true_event(purchased_at < occurred_at)
                   over(partition by s.user_id order by s.occurred_at) as cte 
            from purchases p inner join sessions s 
                 on p.user_id = s.user_id 
     ) a 
     group by a.occurred_at 
     order by 1, 2;
 user_id |     occurred_at     | num_purchases 
---------+---------------------+---------------
     100 | 1959-03-07 04:31:15 |             0
     100 | 1969-03-07 05:31:15 |             2
     200 | 1979-03-07 06:31:15 |             0
     200 | 1989-03-07 07:31:15 |             1
     300 | 1999-03-07 08:31:15 |             0

如何在不支持相关子查询时获得相同的结果

1 个答案: