Question

我必须使用两个表来创建第三个表。 TableA不包含所需的所有信息，因为它仅列出了人们用来了解我们公司的来源，而TableB列出了人们可以使用的所有可能的来源。我希望TableC对未使用的源显示0％。在postgreSQL中这怎么可能？

select "Source", to_char(100 * count(*) / sum(count(*)) over (), '990%') as "The Ratio"
from TableA 
group by "Source";

Source:       The Ratio:

Website         55%
TV              25%
Radio           20%


Select * from Table2:


Source:

Website
TV
Radio
BillBoard
Referral

结果我谦卑地请求帮助：

Source:                The Ratio:

Website                 55%
TV                      25% 
Radio                   20%
BillBoard                0%
Referral                 0%

Answer 1

您只想要一个left join：

select a."Source",
       to_char(100 * count(b.source) / sum(count(*)) over (), '990%') as "The Ratio"
from TableB b left join
     TableA a
     on a.source = b.source
group by a."Source";

Answer 2

左边用table2连接结果：

select t2."Source", to_char(coalesce(t1."The Ratio",0),'990%') "The Ratio"
from table2 t2 left outer join
  (select "Source", 100 * count(*) / sum(count(*)) over ()  "The Ratio"
   from TableA 
   group by "Source") t1
on t1."Source" = t2."Source";

从两个表创建第三个表

2 个答案: