Question

基本上我只是不确定为什么这个查询无法执行：

(SELECT replies.reply_post, replies.reply_content, replies.reply_date AS d, members.username
     FROM (replies) AS a 
        INNER JOIN members ON replies.reply_by = members.id)

            UNION

(SELECT posts.post_id, posts.post_title, posts.post_date AS d, members.username 
     FROM (posts) as b 
        WHERE posts.post_set = 0 
           INNER JOIN members ON posts.post_by = members.id)

ORDER BY d DESC LIMIT 5

我收到了这个错误：

#1064 - 您的SQL语法出错;检查与MySQL服务器版本对应的手册，以获得正确的语法在第2行的'一个INNER JOIN成员ON replies.re'附近

我要做的就是从这两个表中选择5个最近的行（日期）。我已经尝试了Join，union等，我已经看到了很多查询，人们在FROM语句之后放了另一个查询，这对我如何运作没有任何逻辑意义？

我可以肯定地说，您可以从两个不同但已加入的查询中加入同一个表吗？或者我采取了完全错误的方法，因为坦率地说，尽管阅读了错误信息，我似乎无法看到这个查询是如何失败的。

（关于那里的两个查询工作正常）

Answer 1

我认为您的查询中存在语法错误：

FROM (posts) as b 
        WHERE posts.post_set = 0 
           INNER JOIN members ON posts.post_by = members.id)

内部联接应首先出现在条件之前。您的加入条件也是错误的。您需要应用

等条件

INNER JOIN members ON a.reply_by = members.id)
INNER JOIN members ON b.post_by = members.id)

所以你的查询应该是这样的

(SELECT a.reply_post, a.reply_content, a.reply_date AS d, members.username
 FROM (replies) AS a 
 INNER JOIN members ON a.reply_by = members.id)

 UNION

(SELECT b.post_id, b.post_title, b.post_date AS d, members.username 
 FROM (posts) as b 
 INNER JOIN members ON b.post_by = members.id
 WHERE b.post_set = 0)

ORDER BY d DESC LIMIT 5

Answer 2

试试这个：

(SELECT a.reply_post, a.reply_content, a.reply_date AS d, members.username
 FROM replies AS a 
    INNER JOIN members ON a.reply_by = members.id)

        UNION

(SELECT b.post_id, b.post_title, b.post_date AS d, members.username 
 FROM posts as b 
    INNER JOIN members ON b.post_by = members.id 
    WHERE b.post_set = 0)  /* Use where condition after matching Id's using ON */

ORDER BY d DESC LIMIT 5

加入两个选择查询和排序结果

2 个答案: