first_value() over (order by something asc) 应该和 last_value () over (order by something desc) 一样吗？

Question

first_value() 降序排列与 last_value() 升序排列的结果不应该相同吗？我运行以下查询并在查询下方附上了结果。

select random_date, trunc(random_date,'MM') random_month, random_value,
first_value(random_value) over (partition by trunc(random_date,'MM') order by random_date desc) first_,
last_value(random_value) over (partition by trunc(random_date,'MM') order by random_date) last_
from 
(select to_date(round (dbms_random.value (1, 28))
        || '-'
        || round (dbms_random.value (02, 03))
        || '-'
        || round (dbms_random.value (2014, 2014)),
        'DD-MM-YYYY') + level - 1 random_date,
        round(100*(dbms_random.value)) random_value
from dual
connect by level <= 10) order by 2, 1;

Answer 1

您忘记了用于分析函数的移动 window。查看差异（无界前面和无界后面之间使用的行）：

SQL> select random_date, trunc(random_date,'MM') random_month, random_value,
  2  first_value(random_value) over (partition by trunc(random_date,'MM') order by random_date desc rows between unbounded preceding and unbounded following) first_,
  3  last_value(random_value) over (partition by trunc(random_date,'MM') order by random_date rows between unbounded preceding and unbounded following) last_
  4  from
  5  (select to_date(round (dbms_random.value (1, 28))
  6          || '-'
  7          || round (dbms_random.value (02, 03))
  8          || '-'
  9          || round (dbms_random.value (2014, 2014)),
 10          'DD-MM-YYYY') + level - 1 random_date,
 11          round(100*(dbms_random.value)) random_value
 12  from dual
 13  connect by level <= 10) order by 2, 1;

RANDOM_DATE RANDOM_MONTH RANDOM_VALUE     FIRST_      LAST_
----------- ------------ ------------ ---------- ----------
02.02.2014  01.02.2014             93         75         75
09.02.2014  01.02.2014             78         75         75
11.02.2014  01.02.2014             69         75         75
12.02.2014  01.02.2014             13         75         75
21.02.2014  01.02.2014             91         75         75
25.02.2014  01.02.2014             75         75         75
01.03.2014  01.03.2014             54         80         80
15.03.2014  01.03.2014             37         80         80
16.03.2014  01.03.2014             92         80         80
17.03.2014  01.03.2014             80         80         80

10 rows selected

Answer 2

试试这个分析函数。要实现你的目标应该使用 rows between unbounded preceding and unbounded.

first_value(random_value) over (partition by trunc(random_date,'MM') order by random_date desc ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) first_,
last_value(random_value) over (partition by trunc(random_date,'MM') order by random_date ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) last_

完整代码：

select random_date, trunc(random_date,'MM') random_month, random_value,
first_value(random_value) over (partition by trunc(random_date,'MM') order by random_date desc ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) first_,
last_value(random_value) over (partition by trunc(random_date,'MM') order by random_date ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) last_

from 
(select to_date(round (dbms_random.value (1, 28))
        || '-'
        || round (dbms_random.value (02, 03))
        || '-'
        || round (dbms_random.value (2014, 2014)),
        'DD-MM-YYYY') + level - 1 random_date,
        round(100*(dbms_random.value)) random_value
from dual
connect by level <= 10) order by 2, 1;

Answer 3

正如我看到的那样 first_value 这仅用于字符串，但您需要它用于数字，因此将其更改为最小值和最大值在字符串中，10 将在 2 之前，但在数字 2 中，在

之前

first_value() over (order by something asc) 应该和 last_value () over (order by something desc) 一样吗？

Should first_value() over (order by something asc) be the same as last_value () over (order by something desc)?

sql

oracle

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