多级查询从第二个子查询获取值以驱动父元素

Question

我正在尝试获取一个多级查询，以给我提供一个简单的答案。 我有2500行针对邮政编码的数据。 每行包含一个邮政编码，个人的姓名缩写，主要成本和次要成本。 我想根据原始成本获得最低的邮政编码成本-这有点容易-但是，如果对于同一邮政编码，有不止一个人具有相同的原始成本，我需要退还最低成本的那个。 例：

postcode, initials, p_cost, s_cost
AB12    , DS      , 100   , 0
AB12    , JH      , 100   , 40
AB12    , SS      , 120   , 0

因此，从这里开始，我想介绍一下DS，因为它们与JH一起具有最低的主成本，但它们在两者中的辅助成本也最低。 这是到目前为止的SQL：

SELECT initials, min(s_cost) FROM
    (SELECT * FROM MyTable
     WHERE postcode = 'AB12'
     and p_cost = 
        (select min(p_cost) from MyTable 
         WHERE postcode = 'AB12'));

我也尝试过：

SELECT * FROM MyTable
WHERE postcode = 'AB12' 
and p_cost = (select min(p_cost) 
               from MyTable 
               WHERE postcode = 'AB12'
               and s_cost = (select min(s_cost) 
                                     from MyTable 
                                     WHERE postcode = 'AB12'));

有人可以在这里让我摆脱痛苦，这应该很简单，但是距我上次编写SQL和愤怒的SQL已有15年了，这确实困扰了我。

谢谢大家的帮助 ：-）

Answer 1

您是否尝试过使用联接条件作为过滤器将表联接到自身？

select mt1.* 
from mytable mt1
left join mytable mt2 
    on mt1.postcode = mt2.postcode 
        and ( mt1.p_cost < mt2.p_cost 
         or (mt1.p_cost = mt2.p_cost and mt1.s_cost < mt2.s_cost)
        )
where mt1.postcode = 'AB12'

这段代码未经测试。

Answer 2

也许您可以尝试一下。

Select * 
from MyTable 
where postcode = 'AB12' 
order by p_cost asc, s_cost asc 
limit 1;

Answer 3

首先，您需要计算每个邮政编码的最低p_cost是多少

 SELECT postcode, MIN(primary_cost) as min_primary_cost
 FROM MyTable 
 WHERE postcode = 'AB12'

现在，您需要根据“主要费用”计算“ secondary_cost”的最小值

 SELECT primary_cost, MIN(secondary_cost) as min_primary_cost
 FROM MyTable 
 WHERE postcode = 'AB12'
 GROUP BY primary_cost

现在将两者结合在一起

SQL演示

SELECT *
FROM YourTable
JOIN ( SELECT postcode, MIN(primary_cost) as min_primary_cost
       FROM YourTable 
       WHERE postcode = 'AB12'
     ) as p_cost
ON YourTable.postcode = p_cost.postcode
AND YourTable.primary_cost = p_cost.min_primary_cost
JOIN ( SELECT primary_cost, MIN(secondary_cost) as min_secondary_cost
       FROM YourTable 
       WHERE postcode = 'AB12'
       GROUP BY primary_cost
     ) as s_cost
  ON YourTable.primary_cost = s_cost.primary_cost
 AND YourTable.secondary_cost= s_cost.min_secondary_cost
WHERE postcode = 'AB12'