mysql - 表字段的总和，无论用户是否存在

Question

我有一个脚本可以在一个简单的成就类型脚本中计算用户点数，然后按顺序将它们显示在网页上。我有以下 mySQL 函数，但如果用户还没有任何积分（即没有找到“pa.userid”，则根本不会获取用户）

SELECT u.userid,
SUM(IF(pa.plus = '1', pa.points_amount, 0)) - SUM(IF(pa.plus = '0', pa.points_amount, 0)) AS points
FROM awarded_points pa,
users u WHERE u.userid = pa.userid 
GROUP BY u.userid 
ORDER BY points DESC 
LIMIT 10

我将如何使上述代码包含尚未获得任何积分的用户？这是一个复杂的变化吗？

Answer 1

用一个left outer join

SELECT u.userid,
       SUM(IF(pa.plus = '1', pa.points_amount, 0)) - SUM(IF(pa.plus = '0', pa.points_amount, 0)) AS points
FROM users u
LEFT OUTER JOIN awarded_points pa ON u.userid = pa.userid 
GROUP BY u.userid 
ORDER BY points DESC 
LIMIT 10

看到关于连接的精彩解释

Answer 2

使用左连接

SELECT u.userid, 
SUM(IF(pa.plus = '1', pa.points_amount, 0)) - SUM(IF(pa.plus = '0', pa.points_amount, 0)) AS points 
FROM users as u left join awarded_points pa 
ON u.userid = pa.userid  
GROUP BY u.userid  
ORDER BY points DESC  
LIMIT 10