sql - 如何获取最小和最大请求​​的时间？

Question

我有一张包含产品部分的表格。

__________________________________
| SECTION| PRICE |     TIME      |
|--------------------------------|
|  sec1  |   10  | 06-12-17 12:00|
|  sec2  |   20  | 06-12-17 12:01|
|  sec1  |   20  | 06-12-17 12:02|
|  sec1  |   30  | 06-12-17 12:03|
|  sec2  |   30  | 06-12-17 12:04|
----------------------------------

我需要为每个部分设置最小值、最大值和平均值。我做到了。

SELECT MAX(PRICE), MIN(PRICE), AVG(PRICE) FROM table1 GROUP BY SECTION;

我还需要一个最低价和最高价的销售时间。如果最大的销售发生在不同的时间，我需要它们中的任何一个。如何在一张表中获取？

___________________________________________________________
| SECTION| MIN | MAX | AVG |  TIME OF MAX   |  TIME OF MIN |
|----------------------------------------------------------|
|  sec1  | 10  |  30 |  20 | 06-12-17 12:03 |06-12-17 12:00|
|  sec2  | 20  |  30 |  25 | 06-12-17 12:04 |06-12-17 12:01|
-----------------------------------------------------------

Answer 1

在没有三重连接的情况下使用窗口函数:

t=# WITH a as (
SELECT
      SECTION
    , MAX(PRICE) over w
    , MIN(PRICE) over w
    , AVG(PRICE) over w
    , TIME t, price
    , case when MAX(PRICE) over w = price then TIME end maxt
    , case when MIN(PRICE) over w = price then TIME end mint
FROM s154
WINDOW w as (partition by section)
)
select DISTINCT
      SECTION
    , MAX
    , MIN
    , AVG
    , max(maxt) over (partition by section)
    , min(mint) over (partition by section)
from a
;
 section  | max | min |         avg         |         max         |         min
----------+-----+-----+---------------------+---------------------+---------------------
   sec1   |  30 |  10 | 20.0000000000000000 | 2017-06-12 12:03:00 | 2017-06-12 12:00:00
   sec2   |  30 |  20 | 25.0000000000000000 | 2017-06-12 12:04:00 | 2017-06-12 12:01:00
(2 rows)

另外正如 Abelisto 指出的那样，on larger data sets ，在聚合之前过滤结果可以显着降低成本。所以加入

where maxt is not null or mint is not null

推荐到最后。