從多個表中選擇值 - SQL

Question

嗨，我有以下的數據庫結構：

表users包含：email, name

表connections包含：followingemail, followedemail, isfollowedaccept

表locations包含：location, email。

我想要得到的name和我的朋友的的location時：我有我的電子郵件是followingemail的價值，我有我的朋友的電子郵件是followedemail的價值。

應該檢索數據只有當我有一個行中包含我的電子郵件爲followingemail和followedemail我的朋友的電子郵件，也isfollowedaccept是真的connctions表。

我的問題是我該如何編寫該查詢？

我找不出來。謝謝。

Answer 1

試試這個：

select u.name, l.location 
from connections C 
join users U on U.followedemail = C.email 
join location l on l.email = C.email 
where C.followingemail = (your email) 
and U.followedemail = (your friend's email) 
and U.isfollowedaccept = true 

Answer 2

@madalinivascu你寫你需要加入users和locations 2次，每次用於獲取數據，如東西

select 
u1.name as following_name, 
u2.name as followed_name, 
l1.location as following_location, 
l2.location as followed_location 
from connections c 
join users u1 on u1.email = c.followingemail 
join users u2 on u2.email = c.followedemail 
join locations l1 on l1.email = c.followingemail 
join locations l2 on l2.email = c.followedemail 
where 
c.followingemail = '{your email}' 
and c.followedemail = '{friends email}' 
and c. isfollowedaccept = 'true'