SQL 按最近日期选择具有两个唯一列的行

Question

使用以下查询和结果，我正在查找 ChargeId 和 ChargeType 唯一的最新条目。

select chargeId, chargeType, serviceMonth from invoice

    CHARGEID    CHARGETYPE  SERVICEMONTH
1   101         R           8/1/2008
2   161         N           2/1/2008
3   101         R           2/1/2008
4   101         R           3/1/2008
5   101         R           4/1/2008
6   101         R           5/1/2008
7   101         R           6/1/2008
8   101         R           7/1/2008

期望：

    CHARGEID    CHARGETYPE  SERVICEMONTH
1   101         R           8/1/2008
2   161         N           2/1/2008

Answer 1

您可以使用GROUP BY按类型和 id 对项目进行分组。 然后您可以使用MAX()聚合函数来获取最近的服务月份。 下面返回一个带有 ChargeId、ChargeType 和 MostRecentServiceMonth 的结果集

SELECT
  CHARGEID,
  CHARGETYPE,
  MAX(SERVICEMONTH) AS "MostRecentServiceMonth"
FROM INVOICE
GROUP BY CHARGEID, CHARGETYPE

Answer 2

所以这不是请求者所要求的，但它是“SQL 按最近日期选择行”的答案。

修改自http://wiki.lessthandot.com/index.php/Returning_The_Maximum_Value_For_A_Row

SELECT t.chargeId, t.chargeType, t.serviceMonth FROM( 
    SELECT chargeId,MAX(serviceMonth) AS serviceMonth
    FROM invoice
    GROUP BY chargeId) x 
    JOIN invoice t ON x.chargeId =t.chargeId
    AND x.serviceMonth = t.serviceMonth

Answer 3

SELECT chargeId, chargeType, MAX(serviceMonth) AS serviceMonth 
FROM invoice
GROUP BY chargeId, chargeType

Answer 4

我看到大多数开发人员都使用内联查询，而没有注意它对海量数据的影响。

简单来说，您可以通过以下方式实现：

select a.chargeId, a.chargeType, a.serviceMonth 
from invoice a
left outer join invoice b
on a.chargeId=b.chargeId and a.serviceMonth <b.serviceMonth 
where b.chargeId is null
order by a.serviceMonth desc

Answer 5

select to.chargeid,t0.po,i.chargetype from invoice i
inner join
(select chargeid,max(servicemonth)po from invoice 
group by chargeid)t0
on i.chargeid=t0.chargeid

如果不同的费用 ID 具有不同的费用类型组合，则上述查询将起作用。希望这个简单的查询有助于考虑很少的性能时间......

Answer 6

在sqlfiddle演示：

1. 经典方式。

select 
    chargeid, 
    chargetype,
    SERVICEMONTH
from invoice t0
where t0.SERVICEMONTH = (
    select max(SERVICEMONTH) 
    from invoice t1 
    where t1.chargeid = t0.chargeid
    and t1.chargetype = t0.chargetype
);

2. 使用窗口函数。

with w_o as (
    select
        chargeid, 
        chargetype,
        SERVICEMONTH,
        row_number() OVER (PARTITION BY chargeid, chargetype ORDER BY SERVICEMONTH DESC) rn
    from invoice
)
select
    chargeid, 
    chargetype,
    SERVICEMONTH
from w_o
where rn = 1;

很高兴理解并能够使用这两种风格。