得到传递关系的数量

Question

我有3张桌子

客户

• cus_id

站点

• sit_cus_id（来自cus的外键），
• sit_id [一位客户有多个网站]

服务

• ser_sit_id（来自坐的外键），
• ser_id＆amp; nbsp [one site has multiple services]

我希望SQL查询将报告作为

cus_id | # of Sites | # of Services

Answer 1

试试这个：

SELECT C.cus_id, 
       COUNT(DISTINCT S.sit_id) NoOfSites, 
       COUNT(DISTINCT SS.ser_sit_id) NoOfServices
FROM Customer C 
LEFT OUTER JOIN Sites S ON C.cus_id = S.sit_cus_id 
LEFT OUTER JOIN Services SS ON S.sit_id = SS.ser_sit_id 
GROUP BY C.cus_id;