Question

我试图建立一个我不知道的论坛。只是愚弄一些代码。

现在我有两个表，第一个是论坛类别，第二个是论坛板。

我现在的问题是，我可以使用LEFT JOIN或任何连接从类别表中获取每个中的一个，并且所有结果都与来自板的相同catID一起使用吗？

这是我现在没有工作的代码：

$query = $_database->query("
SELECT boards.name AS boardName, boards.info, boards.category, boards.boardID, boards.sort, boards.topics, boards.posts,
categories.catID, categories.name AS catName, categories.sort 
FROM ".PREFIX."forum_boards AS boards LEFT JOIN ".PREFIX."forum_categories AS categories ON boards.category = categories.catID GROUP BY categories.catID ORDER BY boards.boardID");
while ($rad = $query->fetch_array()) {
    echo '<h2>'.$rad['catName'].'</h2>';
    echo $rad['boardName'];
}

请求发布我的表格结构，这里是

董事会：

CREATE TABLE IF NOT EXISTS `mm_forum_boards` (
`boardID` int(11) NOT NULL,
  `category` int(11) NOT NULL DEFAULT '0',
  `name` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `info` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `sort` int(2) NOT NULL DEFAULT '0',
  `topics` int(11) NOT NULL DEFAULT '0',
  `posts` int(11) NOT NULL DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

分类

CREATE TABLE IF NOT EXISTS `mm_forum_categories` (
`catID` int(11) NOT NULL,
  `name` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `info` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `sort` int(11) NOT NULL DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

一些数据：

INSERT INTO mm_forum_categories (`name`, `info`, `sort`) VALUES('Test Cat 1', 'Just giving some lorem data ^^', '1');
INSERT INTO mm_forum_categories (`name`, `info`, `sort`) VALUES('Test Cat 2', 'Just giving some lorem data ^^', '2');
INSERT INTO mm_forum_boards (`category`, `name`, `info`, sort`) VALUES('3', 'Test board 1', 'Lorem board for now', '1');
INSERT INTO mm_forum_boards (`category`, `name`, `info`, sort`) VALUES('3', 'Test board 2', 'Lorem board for now', '2');
INSERT INTO mm_forum_boards (`category`, `name`, `info`, sort`) VALUES('3', 'Test board 3', 'Lorem board for now', '3');

INSERT INTO mm_forum_boards (`category`, `name`, `info`, sort`) VALUES('4', 'Test board 4', 'Lorem board for now', '1')

Answer 1

SQL中的GROUP BY子句在这里是错误的。它使用相同的category_id聚合所有行。当你想要计算它们时这很有用，但不是在这里。

如果您想按类别订购，请将其放在ORDER BY子句

中

Answer 2

按照以下查询

SELECT
  mm_forum_categories.name,
  mm_forum_categories.info,
  mm_forum_boards.name,
  mm_forum_boards.info,
  mm_forum_boards.sort,
  mm_forum_boards.topics
FROM
  mm_forum_categories
LEFT Join mm_forum_boards 
  ON mm_forum_categories.catID = mm_forum_boards.category
WHERE
  mm_forum_categories.catID =  '1'

我认为它会解决你的问题。

Answer 3

据我了解，您需要一个简单的RIGHT OUTER JOIN。看看这个查询。

SELECT mfc.name AS cat_name, mfc.catID as catID
FROM mm_forum_categories mfc
RIGHT OUTER JOIN mm_forum_boards 
ON mfc.catID = mm_forum_boards.category;

如何从一个表中获取一个结果，使用相同的catID从另一个中获取几个结果？

3 个答案: