SQL join left get MAX(date)

Question

我有这些表：

• 通知
  • id INT
  • 日期日期时间
  • ...
    
    
• 主题
  • 身份证
  • 名称
    
    
• notice_theme
  • id_notice
  • id_theme

我想获取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

结果不好。一个主意 ？谢谢。

Answer 1

有很多方法可以解决这个问题，但我已经习惯了这种方式。需要额外的子查询来分别计算每个ID 的最新cDate。

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 Demo