mysql - SQL join left get MAX(date)

Question

我有这些表：

• 注意
  • ID INT
  • 日期日期时间
  • ...
    
    
• 主题
  • ID
  • 姓名
    
    
• 通知主题
  • id_notice
  • id_theme

我想获得每个主题的最新通知。

SELECT id_theme, n.id
FROM notice_theme
LEFT JOIN (
    SELECT id, cdate
    FROM notice
    ORDER BY cdate DESC
) AS n ON notice_theme.id_notice = n.id
GROUP BY id_theme

结果并不好。一个想法 ？谢谢。

Answer 1

有很多方法可以解决这个问题，但我习惯这样做。需要一个额外的子查询来分别计算cDate每个ID.

SELECT  a.*, c.*
FROM    theme a
        INNER JOIN notice_theme b
            ON a.ID = b.id_theme
        INNER JOIN  notice c
            ON b.id_notice = c.ID
        INNER JOIN
        (
            SELECT  a.id_theme, MAX(b.DATE_CREATE) max_date
            FROM    notice_theme a
                    INNER JOIN notice b
                        ON a.ID_Notice = b.ID
            GROUP   BY a.id_theme
        ) d ON  b.id_theme = d.id_theme AND
                c.DATE_CREATE = d.max_date

• SQLFiddle 演示