如何在where子句中使用sum来计算avg

Question

我还是个新手，我刚刚使用了postgresql一个星期。我有点困惑..

我使用NY数据集（http://workshops.opengeo.org/postgis-intro/about_data.html）。

我必须找到一种方法来列出亚洲人口数量多于相应自治市镇平均水平的所有社区，我必须展示亚洲人口的百分比。

我想到这个问题：

select name, 100 * sum(c.popn_asian)/(select (avg(popn_asian)) from nyc_census_blocks group by boroname) 
from nyc_neighborhoods n, nyc_census_blocks c 
where (ST_Contains(n.geom, c.geom) = true) 
and (sum(c.popn_asian)) > (select avg(popn_white) from nyc_census_blocks c1 group by c1.boroname) 

，但我不出声显然where子句后使用总和......我想知道为什么，并学习如何解决这个问题。

感谢

Answer 1

您需要使用having条款针对此问题。

Answer 2

select name, 100 * sum(c.popn_asian)/(select (avg(popn_asian)) from nyc_census_blocks group by boroname) 
from nyc_neighborhoods n, nyc_census_blocks c 
where ST_Contains(n.geom, c.geom) = true 
group by name 
having sum(c.popn_asian) > (select avg(popn_white) from nyc_census_blocks c1 group by c1.boroname)