在SQL中：按相关元素时间戳对唯一元素进行排序

Question

我有两个表“贷款”和“付款”。 贷款具有贷款状态，并可能附带有付款。 付款具有贷款编号，逾期状态和处理日期。

我想获得所有具有loan_status = 1的贷款的清单，这些贷款至少有一项现有的过期= true付款，并按匹配的付款处理日期排序。

以下是一些示例数据：

loan
+----+-------------+
| id | loan_status |
+----+-------------+
| 1  | 0           |
+----+-------------+
| 2  | 1           |
+----+-------------+
| 3  | 1           |
+----+-------------+
| 4  | 1           |
+----+-------------+
| 5  | 1           |
+----+-------------+

payment
+----+---------+----------------+---------------------+
| id | loan_id | overdue_status | processed_date      |
+----+---------+----------------+---------------------+
| 1  | 1       | f              | 2013-07-21 07:00:00 |
+----+---------+----------------+---------------------+
| 2  | 2       | f              | 2013-07-21 08:00:00 |
+----+---------+----------------+---------------------+
| 3  | 3       | f              | 2013-07-21 09:00:00 |
+----+---------+----------------+---------------------+
| 4  | 3       | t              | 2013-07-21 11:00:00 |
+----+---------+----------------+---------------------+
| 5  | 4       | f              | 2013-07-21 06:00:00 |
+----+---------+--------------------------------------+
| 6  | 4       | t              | 2013-07-21 10:00:00 |
+----+---------+----------------+---------------------+
| 7  | 4       | t              | 2013-07-21 13:00:00 |
+----+---------+----------------+---------------------+
| 8  | 5       | t              | 2013-07-21 10:30:00 |
+----+---------+----------------+---------------------+

使用下面的sql查询，我可以找到匹配的贷款，但是，未按处理日期排序：

select id from loan where loan_status = 1 and exists(
    select id from payment where
        payment.loan_id = loan.id and payment.overdue_status = 't')

如何更改上面的SQL查询（或创建新的SQL查询）以按最早的逾期付款（processed_date）订购贷款？

使用上面的数据得到的期望结果应该是：

+----+-------------+
| id | loan_status |
+----+-------------+
| 4  | 1           | // 2013-07-21 10:00:00
+----+-------------+
| 5  | 1           | // 2013-07-21 10:30:00
+----+-------------+
| 3  | 1           | // 2013-07-21 11:00:00
+----+-------------+

Answer 1

SELECT a.id, loan_status from loan_status a 
inner join payment b on a.id = b.loan_id and b.overdue_status = 't' and loan_status = 1
GROUP BY a.id, loan_status, processed_date
ORDER BY processed_date

使用inner join这样您还可以访问其他表中的列。 （好吧，即使您不需要它，如果使用内部联接，您的查询也会更好。无论如何，您所做的实际上是内部联接）

Answer 2

Select a.id, 
      loan_status,
      min(processed_date) as processed_date  
from loan as a 
inner join payment as b 
on a.id = b.loan_id 
and b.overdue_status = 't' and loan_status = 1
Group by a.id,loan_status
Order by processed_date

Answer 3

如果您只是在寻找逾期付款，我认为您根本不需要loan表

select p.*
from (select distinct on (p.loan_id) p.*
      from payment p
      where p.overdue_status = 't'
      order by p.loan_id, p.processed_date
     ) p
order by p.processed_date

如果您只想要状态1贷款：

select p.*
from (select distinct on (p.loan_id) p.*
      from payment p
      where p.overdue_status = 't' and
            p.loan_id in (select l.id from loan where l.status = 1)
      order by p.loan_id, p.processed_date
     ) p
order by p.processed_date;

您可以使用group by而不是distinct on为逻辑。 但是， distinct on我们将第一笔逾期付款的所有属性带入该行。

Answer 4

请尝试以下查询。 上面回答的查询将给出错误，因为必须在select中指定按列名称排序

SELECT Distinct x.id 
FROM 
(
    SELECT  a.id, loan_status, processed_date from loan_status a 
    INNER JOIN payment b on a.id = b.loan_id and b.overdue_status = 't' and loan_status = 1
    ORDER BY processed_date
) x