Sql 如何断言窗口中的当前行是最后一行？

如果我有一个在上有一个

ROW_NUMBER（）的查询，我如何才能得到这个窗口中所有行的输出，或者最后一行作为布尔值

我想在结果中为窗口中的第一行和最后一行创建两列，并使用布尔值

A | ROW_NUMBER
---
1 | 1
2 | 1
2 | 2
3 | 1


TO

A | ROW_NUMBER | FIRST | LAST
---
1 | 1 | 1 | 1
2 | 1 | 1 | 0
2 | 2 | 0 | 1
3 | 1 | 1 | 1

这将为您提供总计数：

COUNT(*) OVER ...

您还可以执行以下操作：

ROW_NUMBER() OVER (.... ORDER BY ... DESC)

按降序排序意味着1=您的最后一条记录这将给出总计数：

COUNT(*) OVER ...

您还可以执行以下操作：

ROW_NUMBER() OVER (.... ORDER BY ... DESC)

按降序排序意味着1=您的最后一条记录
您可以使用
第一个值
：

SELECT A, row_num, 
 CASE WHEN FIRST_VALUE(row_num) OVER(PARTITION BY A ORDER BY row_num) = row_num 
      THEN 1 ELSE 0 END AS first_row,
 CASE WHEN FIRST_VALUE(row_num) OVER(PARTITION BY A ORDER BY row_num DESC)=row_num 
      THEN 1 ELSE 0 END AS last_row  
FROM tab
ORDER BY a, row_num;


输出：

+----+----------+------------+----------+
| a  | row_num  | first_row  | last_row |
+----+----------+------------+----------+
| 1  |       1  |         1  |        1 |
| 2  |       1  |         1  |        0 |
| 2  |       2  |         0  |        1 |
| 3  |       1  |         1  |        1 |
+----+----------+------------+----------+

您可以使用
第一个\u值
：

SELECT A, row_num, 
 CASE WHEN FIRST_VALUE(row_num) OVER(PARTITION BY A ORDER BY row_num) = row_num 
      THEN 1 ELSE 0 END AS first_row,
 CASE WHEN FIRST_VALUE(row_num) OVER(PARTITION BY A ORDER BY row_num DESC)=row_num 
      THEN 1 ELSE 0 END AS last_row  
FROM tab
ORDER BY a, row_num;


输出：

+----+----------+------------+----------+
| a  | row_num  | first_row  | last_row |
+----+----------+------------+----------+
| 1  |       1  |         1  |        1 |
| 2  |       1  |         1  |        0 |
| 2  |       2  |         0  |        1 |
| 3  |       1  |         1  |        1 |
+----+----------+------------+----------+

我会：

select 
  a,
  row_number,
  case ra = 1 then 1 else 0 end as first,
  case rd = 1 then 1 else 0 end as last
from (
  select
    a,
    row_number,
    row_number() over(partition by a order by row_number) as ra,
    row_number() over(partition by a order by row_number desc) as rd
  from my_table
) x
order by a

我会：

select 
  a,
  row_number,
  case ra = 1 then 1 else 0 end as first,
  case rd = 1 then 1 else 0 end as last
from (
  select
    a,
    row_number,
    row_number() over(partition by a order by row_number) as ra,
    row_number() over(partition by a order by row_number desc) as rd
  from my_table
) x
order by a

当你这样说的时候，似乎很明显！干杯。当你这样说的时候，似乎很明显！干杯，太好了，谢谢。喜欢使用
FIRST\u VALUE
。非常好，谢谢。就像使用
第一个\u值一样。