在PostgreSQL数据库中将列转换为行

Question

我当前的查询是：

select rulename,status, count(*)
from triggered_rule_info
group by status, rulename

结果是：

rulename    status  count
eorule1      ack    1
eorule1      open   1
eorule1      close  7
eorule2      open   1
eorule2      ack    1

但我希望结果是：

rulename     ack    open    close
eorule1       1      1       7
eorule2       1      1  

我该如何实现？ 我的PostgreSQL版本是9.4。

Answer 1

为此，您可以使用filter子句：

select rulename
       count(*) filter (where status = 'ack') as ack,
       count(*) filter (where status = 'open') as open,
       count(*) filter (where status = 'close') as closed
from triggered_rule_info
group by rulename
order by rulename;

Answer 2

您可以使用CASE - WHEN和GROUP BY子句来获得所需的结果。 如果status其他值更多，则可能需要添加更多的CASE语句。

范例 ：

SELECT rulename
     , SUM( CASE status WHEN 'ack' THEN 1 ELSE 0 END ) AS "ack"
     , SUM( CASE status WHEN 'open' THEN 1 ELSE 0 END ) AS "open"
     , SUM( CASE status WHEN 'close' THEN 1 ELSE 0 END ) AS "close"
  FROM triggered_rule_info
 GROUP BY rulename
 ORDER BY rulename