如何從一個表中獲取一個結果，並使用相同的catID從另一個表中獲取一個結果？

Question

我試圖建立一種我不知道的論壇。只是玩弄一些代碼。

現在我有兩張桌子，第一個是論壇類別，第二個是論壇板。

我現在的問題是，我可以使用LEFT JOIN或任何連接從類別表中取出其中的每一個，並從板上使用相同的catID獲取所有結果嗎？

這是我現在沒有工作代碼：

$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']; 
} 

有一個請求後我的表結構，這是

板：

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; 

分類：

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; 

一些數據：

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子句在這裏是錯誤的。它聚集具有相同category_id的所有行。當你想數它們時這很有用，但不在這裏。

當您想按類別命令，把它放在ORDER BY條款

Answer 2

按照以下查詢

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' 

這一點，我認爲這將解決您的問題。

Answer 3

據我瞭解，你需要一個簡單的RIGHT OUTER JOIN英寸看看這個查詢。

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;