mysql - SQL 计数给出 1 1 而不是 2

Question

这是我的 SQL 查询

    $sql = "SELECT *, COUNT(seen)
            FROM usr_details 
            WHERE seen=0 AND UserID=3 
            GROUP BY UserID";

    $unread = mysqli_query($DB, $sql);
    $NumberUnread = mysqli_num_rows ($unread);

    echo $NumberUnread;

这是 fiddle http://sqlfiddle.com/#!9/bc3f08/20/0

不是输出 2 它输出 1 1我该如何解决这个问题？

Answer 1

我猜你的问题出在 GROUP BY

当您使用 Group by 时，您需要明确该字段。

SELECT det_id,usr_id,COUNT(seen) 
FROM user_details 
WHERE seen=0 AND usr_id=3
GROUP BY det_id,usr_id