PostgreSQL窗口函数忽略空值

我对PostgreSQL比较陌生，在忽略空值的情况下很难实现lag（）函数。根据文档，不可能简单地将参数传递给函数来实现这一点

有人知道有什么解决办法吗？你可以举出任何一个例子，但如果它有助于你开始：

Col_A   Col_B  Col_A_Lag  Col_B_Lag  ID  Date
VA_1    100    VA_1       100        AA  Jan-1 
null    null   VA_1       100        AA  Jan-2
null    null   VA_1       100        AA  Jan-3
VA_2    250    VA_2       250        AA  Jan-4
VA_2    300    VA_2       300        AA  Jan-5  
null    null   VA_2       300        AA  Jan-6

如果我是从tbl_x中提取，下面是一个简单的SQL脚本：

select
Col_A,
Col_B,
case when Col_A is null then lag(Col_A) over w else Col_A end as Col_A_Lag,
case when Col_B is null then lag(Col_B) over w else Col_B end as Col_B_Lag
from tbl_x
window w as (partition by ID order by Date)

这个脚本不会返回我想要的结果，因为它在延迟中“回望”时包含空值

---

提前谢谢。

我想你不能只是：

select
from tbl_x
window w as (partition by ID order by Date)
where col_a is null;

如果没有，您可能必须：

select
Col_A,
Col_B,
case when Col_A is null
  then (select col_a
          from tbl_x x2
         where x2.id = x1.id
           and col_a is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_A
  end Col_A_Lag,
case when Col_B is null
  then (select col_b
          from tbl_x x2
         where x2.id = x1.id
           and col_b is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_B
  end Col_B_Lag
from tbl_x x1;

---

我想你不能只是：

select
from tbl_x
window w as (partition by ID order by Date)
where col_a is null;

如果没有，您可能必须：

select
Col_A,
Col_B,
case when Col_A is null
  then (select col_a
          from tbl_x x2
         where x2.id = x1.id
           and col_a is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_A
  end Col_A_Lag,
case when Col_B is null
  then (select col_b
          from tbl_x x2
         where x2.id = x1.id
           and col_b is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_B
  end Col_B_Lag
from tbl_x x1;

---

我想你不能只是：

select
from tbl_x
window w as (partition by ID order by Date)
where col_a is null;

如果没有，您可能必须：

select
Col_A,
Col_B,
case when Col_A is null
  then (select col_a
          from tbl_x x2
         where x2.id = x1.id
           and col_a is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_A
  end Col_A_Lag,
case when Col_B is null
  then (select col_b
          from tbl_x x2
         where x2.id = x1.id
           and col_b is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_B
  end Col_B_Lag
from tbl_x x1;

---

我想你不能只是：

select
from tbl_x
window w as (partition by ID order by Date)
where col_a is null;

如果没有，您可能必须：

select
Col_A,
Col_B,
case when Col_A is null
  then (select col_a
          from tbl_x x2
         where x2.id = x1.id
           and col_a is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_A
  end Col_A_Lag,
case when Col_B is null
  then (select col_b
          from tbl_x x2
         where x2.id = x1.id
           and col_b is not null
           and x2.date < x1.date
      order by date desc
         limit 1)
  else Col_B
  end Col_B_Lag
from tbl_x x1;

---

我很感激你的回答，但是当Colu_A发生变化时，你的第二个解决方案不起作用。根据我对“日期”的排序方式，我要么得到列A_滞后中的所有VA_1值，要么得到列A_滞后中的VA_2值。啊，我没有发现这一点逻辑。已编辑查询以将其包括在内。关闭。。。所有空值都用VA_1…填充。。。。最后一个应该是VA_2。谢谢。我很感谢你的回答，但是当上校改变时，你的第二个解决方案不起作用。根据我对“日期”的排序方式，我要么得到列A_滞后中的所有VA_1值，要么得到列A_滞后中的VA_2值。啊，我没有发现这一点逻辑。已编辑查询以将其包括在内。关闭。。。所有空值都用VA_1…填充。。。。最后一个应该是VA_2。谢谢。我很感谢你的回答，但是当上校改变时，你的第二个解决方案不起作用。根据我对“日期”的排序方式，我要么得到列A_滞后中的所有VA_1值，要么得到列A_滞后中的VA_2值。啊，我没有发现这一点逻辑。已编辑查询以将其包括在内。关闭。。。所有空值都用VA_1…填充。。。。最后一个应该是VA_2。谢谢。我很感谢你的回答，但是当上校改变时，你的第二个解决方案不起作用。根据我对“日期”的排序方式，我要么得到列A_滞后中的所有VA_1值，要么得到列A_滞后中的VA_2值。啊，我没有发现这一点逻辑。已编辑查询以将其包括在内。关闭。。。所有空值都用VA_1…填充。。。。最后一个应该是VA_2。谢谢