在Mysql中对表进行分组

Question

我正在尝试创建一个视图，我可以在其中查看租用者名称以及他们从事务表中访问过多少次。在第一个例子中，我不断收到错误＆＃34;子查询返回超过1行＆＃34;。第二个例子给了我租房者ID和访问时间。

 SELECT first_name, last_name,
        (SELECT COUNT(renter_id)
         FROM transactions
         GROUP BY renter_id
        ) AS visited
 FROM renters
 WHERE renter_id IN (SELECT renter_id
                     FROM transactions
                     GROUP BY renter_id
                     having COUNT(renter_id) > 2
                    );


SELECT renter_id, COUNT(renter_id) AS visited
FROM transactions
GROUP BY renter_id
having COUNT(renter_id) > 2;

Answer 1

您正在寻找JOIN。查询如下所示：

SELECT r.first_name, r.last_name, COUNT(*) AS num_visits
FROM transactions t JOIN
     renters r
     ON t.renter_id = r.renter_id
GROUP BY r.first_name, r.last_name 
HAVING COUNT(*) > 2;