pg函数内的for循环答案

【问题标题】：for loop inside pg functionpg函数内的for循环
【发布时间】：2018-05-23 06:55:02
【问题描述】：

我有以下 pg 脚本

create or replace function ended_jobs()
returns table(
 "Time Range" timestamptz,
 "Ended Jobs" numeric
) as $$
begin
return query SELECT date_trunc('HOUR',date_interval) as "Time Range", sum(COALESCE(end_count,0)) "Ended Jobs"  
FROM "job_start_end_rollups"  
right join ( (select   current_timestamp - interval '0 HOUR' date_interval)  
union all (select   current_timestamp - interval '1 HOUR' date_interval) 
union all (select   current_timestamp - interval '2 HOUR' date_interval) 
union all (select   current_timestamp - interval '3 HOUR' date_interval) 
union all (select   current_timestamp - interval '4 HOUR' date_interval) 
union all (select   current_timestamp - interval '5 HOUR' date_interval) 
union all (select   current_timestamp - interval '6 HOUR' date_interval) 
union all (select   current_timestamp - interval '7 HOUR' date_interval) 
union all (select   current_timestamp - interval '8 HOUR' date_interval) 
union all (select   current_timestamp - interval '9 HOUR' date_interval) 
union all (select   current_timestamp - interval '10 HOUR' date_interval) 
union all (select   current_timestamp - interval '11 HOUR' date_interval) 
union all (select   current_timestamp - interval '12 HOUR' date_interval) 
union all (select   current_timestamp - interval '13 HOUR' date_interval) 
union all (select   current_timestamp - interval '14 HOUR' date_interval) 
union all (select   current_timestamp - interval '15 HOUR' date_interval) )  
date_intervals on date_trunc('HOUR', TIMESTAMP WITH TIME ZONE 'epoch' + chunk_start_time * interval '1 millisecond' ) = date_trunc('HOUR',date_interval)   
GROUP BY date_part('HOUR',TIMESTAMP WITH TIME ZONE 'epoch' + chunk_start_time * interval '1 millisecond'),date_interval  
ORDER BY date_interval LIMIT 16;
end;
$$
LANGUAGE 'plpgsql';

运行上面提到的 pg 脚本后，我可以得到数据

select * from ended_jobs()

如何在右连接中写“for循环”以避免多个“联合全部”，像这样

.......
right join ( (select   current_timestamp - interval '0 HOUR' date_interval)
for i in 1..16 loop
union all (select   current_timestamp - concat(i,' HOUR')::INTERVAL date_interval) 
end loop;
........

【问题讨论】：

无关，但是：您不需要plpgsql。一个简单的SQL function 就足够了。另外：语言名称是一个标识符，不要把它放在单引号中：它应该是language plpgsql

标签： postgresql for-loop plpgsql

【解决方案1】：

您可以为此使用generate_series()：

FROM "job_start_end_rollups"  
  right join generate_series(current_timestamp - interval '15 HOUR',
                             current_timestamp, 
                             interval '1 hour') as date_intervals(date_interval) 
             ON ....

您也可以将date_trunc() 移到其中：

right join (
  select date_trunc('HOUR',di) as date_interval
  from generate_series(current_timestamp - interval '15 HOUR',
                       current_timestamp, 
                       interval '1 hour') as t(di)
) as date_intervals ON .... = date_intervals.date_interval

【讨论】：

@KhachaturSaribekyan：如果这解决了您的问题，请接受答案，以便将您的问题标记为已解决。