mysql - 获取每个类别 10 条最新记录，甚至有些记录少于 10 条

Question

这是我的表格的示例:

+-----+-----+------------+--------+-------------+--------------+
| LID | AID | Created    | TypeID | PaymentDate | PaymentValue |
+-----+-----+------------+--------+-------------+--------------+
| 1   | 529 | 2017-05-12 | 1      | 2017-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 2   | 529 | 2018-04-10 | 4      | 2018-04-10  | 200          |
+-----+-----+------------+--------+-------------+--------------+
| 3   | 441 | 2014-01-23 | 3      | 2014-01-23  | 300          |
+-----+-----+------------+--------+-------------+--------------+
| 4   | 324 | 2017-09-14 | 1      | 2017-09-14  | 400          |
+-----+-----+------------+--------+-------------+--------------+
| 5   | 111 | 2018-05-12 | 0      | 2018-05-12  | 340          |
+-----+-----+------------+--------+-------------+--------------+
| 6   | 529 | 2018-05-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 7   | 529 | 2018-06-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 8   | 529 | 2018-07-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 9   | 529 | 2018-08-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 10  | 529 | 2018-09-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 11  | 529 | 2018-01-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 12  | 529 | 2018-05-14 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 13  | 529 | 2018-05-21 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+
| 14  | 529 | 2018-03-12 | 1      | 2018-05-12  | 100          |
+-----+-----+------------+--------+-------------+--------------+

这是另一个表

+-----+-------+
| ID  |caption|
+-----+-------+
| 0   | bad   |
+-----+-------+
| 1   | good  |
+-----+-------+

我需要为每个 AID 获取 10 条最新记录。如果某些 AID 的记录少于 10 条，我需要获取 10 行，并将“无付款日期”放入 PaymentDate 和 Created 字段中，将 Null 放入 TypeID 中，将 0 放入 PaymentValue 中。我可以获得 10 条或更少的最新记录

select *
from (select *,
         (@rn := if(@c = AID, @rn + 1,
                    if(@c := AID, 1, 1)
                   )
         ) as rn
from history cross join
       (select @rn := 0, @c := -1) params
order by AID, Created desc
) t
having rn <= 10;

但我不知道如何强制 mysql 为每个 AID 输出 10 行。请帮助我。

结果应采用表格形式
AID、类型Id、已创建、标题

Answer 1

我已经做到了。此查询需要创建一行 10 条记录，以与表中不同的 AID 值组合。我能够显示金额和创建日期的结果，并让您继续，因为您会明白的。关键部分是构建一个包含 10 行乘以不同 AID 的表，因此表 r 中有大约 40 行。然后对表 t 进行左连接，这与您所做的类似。表 t 最多获得 10 条记录的排名。任何缺失的排名最多 10 个建议将由表 r 填充。 Coalesce 将分配默认值，例如金额为 0，日期为“无创建日期”。

http://sqlfiddle.com/#!9/855c21/2

SELECT coalesce(r.aid, t.aid) as aid,
   coalesce(t.paymentvalue, 0) as paymentvalue,
   coalesce(cast(t.created as char), 'no create date') as created
FROM (select * from (
 select 1 as rw union
  select 2 union select 3 
  union select 4 union select 5
  union select 6 union select 7
  union select 8 union select 9
  union select 10) u
 cross join (select distinct aid
     from history) h
   ) as r
LEFT JOIN (
SELECT a.aid, a.paymentvalue, 
  a.created, count(*) rn
FROM history a
JOIN history b 
ON a.aid = b.aid
AND a.created <= b.created
GROUP BY a.aid, a.created
HAVING COUNT(*) <= 10) t
on r.rw=t.rn and r.aid=t.aid
order by aid, created;