php - 如何按列名分组并确保查询检索到最后更新

Question

我目前正在使用 MySQL 创建一个将返回以下内容的 View :

NAME | EMAIL | LAST_SEEN

abby | a@l.d | 2015-10-31 14:36:26
abby | a@l.d | 2015-11-28 13:30:37

然后我将 GROUP BY name 应用于 select query 并返回以下内容

 NAME | EMAIL | LAST_SEEN

 abby | a@l.d | 2015-10-31 14:36:26

我想知道如何修复此查询，使其返回以下内容:

NAME | EMAIL | LAST_SEEN

abby | a@l.d | 2015-11-28 13:30:37

实际代码如下:

CREATE VIEW v_user_last_seen
AS
SELECT concat_ws(' ', u.first_name, u.middle_name, u.last_name) AS user_name
    ,c.email
    ,l.in_when AS last_seen
FROM user AS u
INNER JOIN check_here_first AS c ON c.email = u.email
INNER JOIN log AS l ON l.u_id = c.username
GROUP BY user_name
ORDER BY user_name ASC

Answer 1

只需使用 max(last_seen)

 select name, email, max(last_seen) 
 from  yourtable,
 group by name, email;