Question

这是我对getting-the-last-record-inserted-into-a-select-query

的另一个问题的跟进

我正在尝试编辑一个查询，Andrea非常友好地帮助我昨天哪个页面工作得很好，但是我试图创建一个类似的查询而没有太多运气。

我需要的是每个电路板显示电路板名称，与该电路板相关的主题和消息的数量以及最后一条消息的用户，主题和日期（确实有效）

我需要的是获取电路板名称，主题和消息计数

这是我的表结构

CREATE TABLE `boards` (
  `boardid` int(2) NOT NULL auto_increment,
  `boardname` varchar(255) NOT NULL default '',
  PRIMARY KEY  (`boardid`)
);

CREATE TABLE `messages` (
  `messageid` int(6) NOT NULL auto_increment,
  `topicid` int(4) NOT NULL default '0',
  `message` text NOT NULL,
  `author` varchar(255) NOT NULL default '',
  `date` datetime(14) NOT NULL,
  PRIMARY KEY  (`messageid`)
);

CREATE TABLE `topics` (
  `topicid` int(4) NOT NULL auto_increment,
  `boardid` int(2) NOT NULL default '0',
  `topicname` varchar(255) NOT NULL default '',
  `author` varchar(255) NOT NULL default '',
  PRIMARY KEY  (`topicid`)
);

以及我根据Andrea为我做的查询得出的查询。此查询在boardname中输出的内容，主题和消息的数量（即使有5个也是1），主题作者和messagecount（不需要），作者和最后一篇文章的日期（需要））但不是所需的主题名称

SELECT b.boardname, count( DISTINCT t.topicname ) AS topics, count( lm.message ) AS message, t.author as tauthor, 

      (select count(message) from messages m where m.topicid = t.topicid) AS messagecount, 
       lm.author as lauthor, lm.date
  FROM topics t
  INNER JOIN messages lm
    ON lm.topicid = t.topicid AND lm.date = (SELECT max(m2.date) from messages m2)
  INNER JOIN boards b
    ON b.boardid = t.boardid
  GROUP BY t.topicname

这是我的原始查询，它可以完成我想要的但是获得第一个帖子，而不是最后一个

SELECT b.boardid, b.boardname, count( DISTINCT t.topicname ) AS topics, count( m.message ) AS message, m.author AS author, m.date AS date, t.topicname AS topic
FROM boards b
INNER JOIN topics t ON t.boardid = b.boardid
INNER JOIN messages m ON t.topicid = m.topicid
INNER JOIN (

SELECT topicid, MAX( date ) AS maxdate
FROM messages
GROUP BY topicid
) test ON test.topicid = t.topicid
GROUP BY boardname
ORDER BY boardname

对此非常感激的任何帮助

Answer 1

您需要根据ORDER BY子句定义“LAST”。完成后，您只需撤消订单的方向，然后将LIMIT 1添加到查询中。

Answer 2

SELECT  b.*, m.*, t,*
        (
        SELECT  COUNT(*)
        FROM    topics ti
        WHERE   ti.boardid = b.boardid
        ) AS topiccount,
        (
        SELECT  COUNT(*)
        FROM    topics ti, messages mi
        WHERE   ti.boardid = b.boardid
                AND mi.topicid = ti.topicid
        ) AS messagecount
FROM    boards b
LEFT JOIN
        messages m
ON      m.messageid = (
        SELECT  mii.messageid
        FROM    topics tii, messages mii
        WHERE   tii.boardid = b.boardid
                AND mii.topicid = tii.topicid
        ORDER BY
                mii.date DESC
        LIMIT 1
        )
LEFT JOIN
        topics t
ON      t.topicid = m.topicid

获取select查询中表的最后一条记录

2 个答案: