SQL Snowflake FILTER 函数 - 有条件地更新行

Question

我正在尝试编写一个查询，在该查询中我根据其他条件更新计数器。例如：

with table1 as (select *, count from table1)

select box_type, 
case when box_type = lag(box_type) over (order by time) 
then 
  count, update table1 set count = count + 1
else
  count
end as identifier

这是我正在尝试做的基本要点。我想要一个如下所示的表格：

box_type    identifier
small        1
small        1
small        1
medium       2
medium       2
large        3
large        3
small        4

我最初需要在 Postgresql 中执行此操作。解决办法是

select t1.*,
       count(*) filter (where box_type is distinct from prev_box_type) over (order by time) as count
from (select t1.*,
             lag(box_type) over (order by time) as prev_box_type
      from table1 t1
     ) t1

但我无法让它在 Snowflake 语法中工作。

谢谢！

Answer 1

一种方法是：

select t1.*,
       sum(case when box_type is distinct from prev_box_type then 1 else 0 end) over (order by time) as count
from (select t1.*,
             lag(box_type) over (order by time) as prev_box_type
      from table1 t1
     ) t1;

或者更简单地说：

select t1.*,
       sum( (box_type is distinct from prev_box_type)::int ) over (order by time) as count

或者内置函数conditional_change_event()：

select t1.*,
       conditional_change_event(box_type) over (order by time) as count
from table1 t1;