postgresql复杂查询连接同一个表

Question

我想从过去6个月未创建任何交易的表'交易'中获取这些客户。

表：

'transactions'
id, email, state, paid_at

要想象：

|------------------------ time period with all transactions --------------------|
|-- period before month transactions > 0) ---|---- curr month transactions = 0 -|

我想这是可行的，只有那些在右侧没有任何交易的联接。

实施例： 月=十一月

左侧的条件应为：

1. COUNT（l.id）＆gt; 0
2. l.paid_at＆lt; '2013-05-01 00:00:00'

右侧的条件：

1. COUNT（r.id）= 0
2. r.paid_at BETWEEN'2013-05-01 00:00:00''''2013-11-30 23:59:59'

加入正确的方法吗？

答案

SELECT
    C .email
FROM
    transactions C
WHERE
    (
        C .email NOT IN (
            SELECT DISTINCT
                email
            FROM
                transactions
            WHERE
                paid_at >= '2013-05-01 00:00:00'
            AND paid_at <= '2013-11-30 23:59:59'
        )
        AND
        C .email IN (
            SELECT DISTINCT
                email
            FROM
                transactions
            WHERE
                paid_at <= '2013-05-01 00:00:00'

        )
    )
AND c.paid_at <= '2013-11-30 23:59:59'

Answer 1

有几种方法可以做到这一点。使用子查询为过去6个月内的事务获取不同的客户ID，然后选择其id不在子查询中的客户。

select c.id, c.name
from customer c
where c.id not in (select distinct customer_id from transaction where dt between <start> and <end>);

或者，使用从客户到事务的左连接，并过滤结果以使事务标识为null。左连接包括左侧表中的所有行，即使右侧表中没有匹配的行也是如此。左边连接的解释：http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html

select c.id, c.name
from customer c
    left join transaction t on c.id = t.customer_id
          and t.dt between <start> and <end>
where t.id is null;

左连接方法可能更快。