sql - 从两个表创建第三个表

Question

我必须利用两个表来创建第三个表。表 A 没有包含所有需要的信息，因为它只列出了人们用来了解我们公司的来源，而表 B 列出了人们可以利用的所有可能来源。我希望 TableC 为未使用的源显示 0%。这在 postgreSQL 中怎么可能？

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

结果我谦虚地请求帮助:

Source:                The Ratio:

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

Answer 1

像这样将结果与 table2 左连接:

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";