选择语句中的更新语句

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 table 1 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

我只想在 box_type 每次更改时递增该标识符值

谢谢！

Answer 1

只有当您有一个指定排序的列时，您的问题才有意义。让我假设存在这样一个列 - 根据您的代码，我将其命名为 time。

然后，您可以使用lag() 和累积和：

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