Question

select n.l_id, n.fromorto, DATE(dtime),avg(mean_speed) as ms_sat_t
from newdataa n
inner join majhwys as m
on n.l_id = m.link_id
where n.day_number=6 and n.fromorto='T'
group by n.fromorto,CAST(dtime as DATE),n.l_id
order by n.l_id

在where子句中可以有四个组合，第6/7天，以及fromorto-F / T。我必须编写4个单独的查询，有没有一种方法可以编写一个包含4列（ms_sat_f，ms_sat_t，ms_sun_f，ms_sun_t）的查询。我不太确定要编写子查询。任何帮助，将不胜感激。

Answer 1

您可以将条件聚合与filter子句一起使用：

select n.l_id, n.fromorto, DATE(dtime),
       avg(mean_speed) filter (where n.day_number = 6 and n.fromorto = 'T') as ms_sat_t,
       avg(mean_speed) filter (where n.day_number = 6 and n.fromorto = 'F') as ms_sat_f,
       avg(mean_speed) filter (where n.day_number = 7 and n.fromorto = 'T') as ms_sun_t,
       avg(mean_speed) filter (where n.day_number = 7 and n.fromorto = 'F') as ms_sun_f
from newdataa n inner join
     majhwys m
     on n.l_id = m.link_id
group by n.fromorto, CAST(dtime as DATE), n.l_id
order by n.l_id;

在旧版本的Postgres中，您可以使用条件聚合来实现此目标：

avg(case when n.day_number = 6 and n.fromorto = 'T' then mean_speed end) as ms_sat_t,

group by子句Postgres

1 个答案: