Question

我有一个SQL查询，我试图只显示不同的记录，如每个用户订单的最后一个帖子desc。怎么做？我尝试了分组，但它失败了。

SELECT jca.id,
ju.name,
jca.actor,
jca.title as title,
jca.created as postedDate
FROM community_activities jca 
left join users ju on jca.actor=ju.id
left join community_users jcu on jcu.userid=ju.id 
ORDER BY jca.id, jca.postedDate DESC LIMIT 0 , 50;


id  name    actor   title   
200     chandra 12      hello man
201     chandra 12      hey man
202     shayam  13      hello hero
203     chandra 12      hello yoyo
204     kokila  16      yep
205     chandra 12      hello y
206     chandra 12      hello  abc

Answer 1

SELECT 
    MAX(jca.id),     -- just selects maximum of each column , 
    DISTINCT ju.name, -- max() may be wrong for your scenario .
    MAX(jca.actor),
    MAX(jca.title) as title,
    MAX(jca.created) as postedDate
FROM 
    community_activities jca 
left join 
    users ju on jca.actor=ju.id
left join 
    community_users jcu on jcu.userid=ju.id 
GROUP BY 
    ju.name;

输出：

202     shayam  13      hello hero

204     kokila  16      yep

206     chandra 12      hello  abc

Answer 2

要仅显示每个用户的最新帖子，请创建一个派生表，该表仅包含每个用户的最新帖子ID，并将community_activities加入该表，因此只会显示这些结果。

SELECT jca.id,
ju.name,
jca.actor,
jca.title as title,
jca.created as postedDate
FROM community_activities jca 

JOIN (SELECT MAX(id) max_id
FROM community_activities 
GROUP BY actor) t1 on t1.max_id = jca.id

LEFT JOIN users ju on jca.actor=ju.id
LEFT JOIN community_users jcu on jcu.userid=ju.id 
ORDER BY jca.id, jca.postedDate DESC LIMIT 0 , 50;

Answer 3

SELECT      jca.id,
            ju.name,
            jca.actor,
            jca.title AS title,
            MAX(jca.created) AS postedDate
FROM        community_activities jca 
LEFT JOIN   users ju ON (jca.actor = ju.id)
LEFT JOIN   community_users jcu ON (jcu.userid = ju.id)
ORDER BY    jca.created DESC

Sql Query显示不同的记录

3 个答案: