SQL连接左边得到MAX（日期）

Question

i have these tables :

• notice
  • id INT
  • cdate DATETIME
  • ...
    
    
• theme
  • id
  • name
    
    
• notice_theme
  • id_notice
  • id_theme

I want to get the latest notices for each theme.

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

The result is not good. An idea ? Thanks.

Answer 1

There are so many ways to solve this but I'm used to do it this way. An extra subquery is needed to separately calculate the latest cDate for every 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 Demo