Question

表结构

CREATE TABLE IF NOT EXISTS `blogs` (
  `id` int(11) NOT NULL auto_increment,
  `title` text collate utf8_bin NOT NULL,
  `content` longtext collate utf8_bin NOT NULL,
  `active` tinyint(4) NOT NULL default '0',
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_bin AUTO_INCREMENT=2768 ;

CREATE TABLE IF NOT EXISTS `pics` (
  `id` int(11) NOT NULL auto_increment,
  `blogid` int(11) NOT NULL default '0',
  `islogo` tinyint(4) NOT NULL default '0',
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_bin AUTO_INCREMENT=4132 ;

CREATE TABLE IF NOT EXISTS `vdos` (
  `id` int(11) NOT NULL auto_increment,
  `blogid` int(11) NOT NULL default '0',
  `file` varchar(255) collate utf8_bin NOT NULL,
  `title` varchar(255) collate utf8_bin NOT NULL,
  `description` text collate utf8_bin NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_bin AUTO_INCREMENT=3759 ;

查询

select distinct b.id from blogs b 
left join pics p ON b.id = p.blogid 
left join vdos v ON b.id = v.blogid 
where p.islogo = '0' and b.`active` = '1'

我打算做的是列出包含图片或视频的博客ID。这个查询的作用是它只列出有图片的博客，而不列出只有视频的博客ID。

谁能看到我做错了什么？

Answer 1

那是因为你设置了pics.islogo为'0'的条件。没有图片的博客永远不会是'0'。将条件移动到连接：

select distinct b.id from blogs b 
left join pics p ON b.id = p.blogid and p.islogo = '0'
left join vdos v ON b.id = v.blogid
where b.`active` = '1'

Answer 2

p.islogo只会导致带有图片的博客。你必须要做

where p.islogo = '0' and b.`active` = '1' or p.islogo IS NULL

还要匹配没有图片的博客。

编辑：抱歉，最初误读了这个问题。 where子句应该更改为

WHERE (p.islogo = "0" AND p.id IS NOT NULL) OR (v.id IS NOT NULL)

Answer 3

select from blogs b 
left join pics p ON b.id = p.blogid 
left join vdos v ON b.id = v.blogid 
where p.islogo = '0' and b.`active` = '1' GROUP BY b.id;

MySQL Query无法从2个连接表中正确选择

表结构

查询

3 个答案: