我正在PostgreSQL数据库上写一个查询,并且不知道如何在连接后执行非空值的计数。在MySQL中我会写:postgresql vs mysql左连接
select count(a.clicker_id), count(b.clicker_id) from
(select * from events where type='click') a
left join (select * from tbl_events where type='conversion')b
on a.clicker_id=b.clicker_id
基本上,试图写没有一个子查询如下:
select date(cl.created_at), count(cl.click_id) as clicks, count(cp.click_id) as Conversions from events_table cl
left outer join (select click_id, created_at from events_table where type='conversion_potential')cp
on (cl.click_id=cp.click_id)
where cl."type"='click'
and cl.placement_id in (1,2,3)
group by 1
由于你的'b.type = conversion'子句,你事实上正在做一个内部连接。仔细检查你的MySQL查询是否是你发布的。 – 2013-05-07 12:18:48
刚刚删除我的答案,因为是错的。 – fog 2013-05-07 12:35:42
在_RIGHT_查询中是否真的有两个表,事件和tbl_events? – 2013-05-07 13:05:36