如何在Postgres中通过分区实现Oracle计数（独特）

Question

这是我在选择语句中的sql示例。从oracle转换为postgres，需要一种简单的方法来重新实现Oracle数据在postgres中的分区。

, count(distinct on pm.mobseg_state) over (partition by pm.trans_id) as mob_segments_count 
, count(distinct on pm.country_reg_region_cd) over (partition by pm.trans_id) as countries_count 

Answer 1

Postgres不直接支持count(distinct)。但是你可以用子查询来实现它：

select . . ., 
     sum((seqnum_tm = 1)::int) as mob_segments_count , 
     sum((seqnum_tr = 1)::int) as countries_count 
from (select . . ., 
      row_number() over (partition by pm.trans_id, pm.country_reg_region_cd order by pm.country_reg_region_cd) as seqnum_tr, 
      row_number() over (partition by pm.trans_id, pm.mobseg_state order by pm.pm.mobseg_state) as seqnum_tm 
     . . . 
    ) . . . 

这个想法很简单。根据partition by键和不同的列计算row_number()。然后，只需加上值为“1”的次数。这需要一个子查询，因为你不能嵌套窗口函数。