查找使用SQL接受的好友請求的一小部分？

我有兩個社交網站的表格 - 一個包含發送的所有好友請求的發件人和收件人的名稱，另一個包含接受的所有好友請求的發件人和收件人的名稱。我創建了一個虛擬數據庫，內容如下 -查找使用SQL接受的好友請求的一小部分？

CREATE TABLE requested (sender text(10), receiver text(10)); 
INSERT INTO requested (sender, receiver) VALUES ('tom', 'jerry'); 
INSERT INTO requested (sender, receiver) VALUES ('tom', 'adam'); 
INSERT INTO requested (sender, receiver) VALUES ('tom', 'alice'); 
INSERT INTO requested (sender, receiver) VALUES ('anne', 'jack'); 
INSERT INTO requested (sender, receiver) VALUES ('anne', 'bill'); 

CREATE TABLE accepted (sender text(10), receiver text(10)); 
INSERT INTO accepted (sender, receiver) VALUES ('tom', 'jerry'); 
INSERT INTO accepted (sender, receiver) VALUES ('tom', 'alice'); 
INSERT INTO accepted (sender, receiver) VALUES ('anne', 'jack');

如何顯示爲每個用戶接受的好友請求分數？對於這些表，我想看到類似 -

tom | 0.6666 
anne | 0.5

來源

2017-05-21 Tim

你似乎沒有主鍵 - 這可能會在適當的時候出現問題 – Strawberry

FWIW，我不會做一個單獨的互換表。 – Strawberry

@Strawberry我同意。這個問題是從「實習面試」問題清單中取得的。 – Tim

SELECT 
     sender, 
     count(*)/(SELECT count(*) FROM requested 
            WHERE requested.sender = accepted.sender) as 'ratio' 
    FROM accepted group by sender

SELECT 
     sender, 
     (SELECT count(*) FROM accepted 
         WHERE requested.sender = accepted.sender)/count(*) as 'ratio' 
    FROM requested group by sender

頂一個我會gnore發件人，至少沒有一個回覆。底部的查詢將顯示這些。

來源

2017-05-21 03:21:19

使用兩個表之間的外連接，讓你得到所有從「要求」表格中的行，只有匹配行從「接受」表：

select 
    r.sender, 
    r.receiver, 
    sum(case when a.sender is not null then 1 else 0 end)/count(*) as fraction 
from 
    requested as r 
    left join accepted as a 
     on a.sender=r.sender 
     and a.receiver=r.reciever 
group by 
    r.sender, 
    r.receiver;

來源

2017-05-21 03:15:36

查找使用SQL接受的好友請求的一小部分？

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