sql在am / n關系中計數多個列

Question

我正在努力處理三個相關的表，在這些表中我想顯示使用特定代碼的域 數和地址數 。 我有三個表：

table_locations ：

ID | domain       | address             
======================================
 1 | example.com  | example.com/siteA   
 2 | example.com  | example.com/siteB   
 3 | example.com  | sub.example.com     
 4 | whatever.com | whatever.com 
 5 | foobar.com   | foobar.com/site123  
 6 | foobar.com   | foobar.com/site     

table_codes ：

ID | code        
==========
 1 | ABC 
 2 | DEF  

table_codes_locations ：

code_id | location_id        
=====================
 1      | 1 
 1      | 2    
 1      | 3
 1      | 4
 2      | 5 
 2      | 6 

我想得到的內容（編輯：將查詢限制為address ='example.com'時）：

ID | code  | domaincount | addresses      
=====================================
 1 | ABC   |  2          | 3
 2 | DEF   |  1          | 2

這意味着代碼“ ABC”用於一個域（example.com）和三個子域； “ DEF”用於一個域和兩個子域

domaincount顯示使用代碼的域的數量，而地址顯示使用代碼的給定域的地址的數量。 我不確定是否僅用一條語句就能做到

Answer 1

您可以使用count(distinct)來做到這一點：

select c.code, count(distinct l.domain) as numdomains,
       count(l.address) as numaddress
from codes c left outer join
     code_locations cl
     on c.id = cl.code_id left outer join
     locations l
     on l.id = cl.location_id
group by c.code;

編輯：

也許：

select c.code, count(distinct l.domain) as numdomains,
       count(l.address) as numaddress,
       sum(case when l.address like '%example.com% then 1 else 0 end) as NumAddressExample
from codes c left outer join
     code_locations cl
     on c.id = cl.code_id left outer join
     locations l
     on l.id = cl.location_id
group by c.code;