PHP和mySQL:重复输入问题 - 需要每个条目只显示一次,但它们会重复

Question

我的平台:

PHP和mySQL

我在这里:

我有4个表,即'books','book_type','book_categories','all_categories'.

我在做什么:

简单来说,我想显示库存中的所有书籍,即in_stock ='y',所有书中的书籍相关信息,只需一次,不重复输入.目前每本书都是重复的,我只想展示一次.

当前的问题:

在我的应用程序的前端,实际上当我希望它们只出现一次时(如在DISTINCT/UNIQUE中)并且不重复它们时,条目会反复显示.

我的怀疑:

我怀疑重复数据是因为每本书所属的类别.每个单一的图书条目都会多次显示,因为它属于一个类别.混乱？我的意思是,如果book1属于4个类别,那么book1将显示4次.如果book2属于2个类别,则显示2次.

我需要的:

我需要PHP和mySQL代码来解决上述问题.我希望我们可以在不使用mySQL中的GROUP_CONCAT的情况下解决问题,因为有相同的限制(1024？).一本书可以属于许多类别,我不想冒着使用GROUP_CONCAT丢失任何数据的风险.我还希望在单个查询中执行此操作,而无需在循环中重复访问数据库.感谢您的理解.

所有表和复制问题的相应数据如下:

CREATE TABLE IF NOT EXISTS `books` (
  `book_id` int(11) NOT NULL auto_increment,
  `book_type_id` int(11) NOT NULL,
  `book_title` varchar(50) NOT NULL,
  `book_price` smallint(4) NOT NULL,
  `in_stock` char(1) NOT NULL,
  PRIMARY KEY  (`book_id`),
  KEY `book_type_id` (`book_type_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

--
-- Dumping data for table `books`
--

INSERT INTO `books` (`book_id`, `book_type_id`, `book_title`, `book_price`, `in_stock`) VALUES
(1, 1, 'My Book 1', 10, 'y'),
(2, 1, 'My Book 2', 20, 'n'),
(3, 2, 'My Book 3', 30, 'y'),
(4, 3, 'My Book 4', 40, 'y'),
(5, 2, 'My Book 5', 50, 'n'),
(6, 1, 'My Book 6', 60, 'y'),
(7, 3, 'My Book 7', 70, 'n'),
(8, 2, 'My Book 8', 80, 'n'),
(9, 1, 'My Book 9', 90, 'y'),
(10, 3, 'My Book 10', 100, 'n');

--
-- Table structure for table `book_type`
--

CREATE TABLE IF NOT EXISTS `book_type` (
  `book_type_id` int(11) NOT NULL auto_increment,
  `book_type` varchar(50) NOT NULL,
  PRIMARY KEY  (`book_type_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

--
-- Dumping data for table `book_type`
--

INSERT INTO `book_type` (`book_type_id`, `book_type`) VALUES
(1, 'Good'),
(2, 'Better'),
(3, 'Best');


--
-- Table structure for table `book_categories`
--

CREATE TABLE IF NOT EXISTS `book_categories` (
  `book_id` int(11) NOT NULL,
  `cat_id` int(11) NOT NULL,
  PRIMARY KEY  (`book_id`,`cat_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `book_categories`
--

INSERT INTO `book_categories` (`book_id`, `cat_id`) VALUES
(1, 1),
(1, 2),
(1, 3),
(1, 4),
(1, 5),
(2, 1),
(2, 2),
(3, 1),
(3, 2),
(3, 3);


--
-- Table structure for table `all_categories`
--

CREATE TABLE IF NOT EXISTS `all_categories` (
  `cat_id` int(11) NOT NULL auto_increment,
  `category` varchar(50) NOT NULL,
  PRIMARY KEY  (`cat_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

--
-- Dumping data for table `all_categories`
--

INSERT INTO `all_categories` (`cat_id`, `category`) VALUES
(1, 'Comedy'),
(2, 'Drama'),
(3, 'Romance'),
(4, 'Horror'),
(5, 'Trivia'),
(6, 'Puzzles'),
(7, 'Riddles'),
(8, 'Kids'),
(9, 'Gents'),
(10, 'Ladies');

我的目标:

//MY QUERY:
SELECT books.book_title,  books.book_price,
       book_type.book_type,
       all_categories.category
FROM books 
LEFT JOIN book_type       ON books.book_type_id = book_type.book_type_id
LEFT JOIN book_categories ON books.book_id = book_categories.book_id
LEFT JOIN all_categories  ON book_categories.cat_id = all_categories.cat_id
WHERE books.in_stock = 'y' 

当前输出:

book_title  book_price  book_type       category
My Book 1    10          Good            Comedy
My Book 1    10          Good            Drama
My Book 1    10          Good            Romance
My Book 1    10          Good            Horror
My Book 1    10          Good            Trivia
My Book 3    30          Better          Comedy
My Book 3    30          Better          Drama
My Book 3    30          Better          Romance
My Book 4    40          Best            NULL
My Book 6    60          Good            NULL
My Book 9    90          Good            NULL

需要以下输出:

book_title  book_price  book_type       category
My Book 1    10          Good            Comedy, Drama, Romance, Horror, Trivia
My Book 3    30          Better          Comedy, Drama, Romance
My Book 4    40          Best            NULL
My Book 6    60          Good            NULL
My Book 9    90          Good            NULL

感谢所有提前.

Answer 1

确保不会丢失任何数据的最佳方法是多次查询。单独查询表并在 PHP 中连接它们，可能这样你的查询看起来像这样

book_id book_title  book_price  book_type         
    1  My Book 1    10          Good           
    2  My Book 3    30          Better          
    3  My Book 4    40          Best           
    4  My Book 6    60          Good            
    5  My Book 9    90          Good           

    book_id, category
    1   Comedy
    1   Drama
    1   Romance
    2   Comedy

ETC

编辑：

不，您不需要在数据库上获得 100 次点击，只需两次，一次获得书籍，下一次获得类别。循环将在 PHP 中完成，以循环第二个查询并将数据与第一个查询连接起来。第二个查询可能是

SELECT book.book_id, all_categories.category FROM book_category JOIN all_categories on book_categories.cat_id=all_categories.cat_id JOIN books on books.book_id=book_categories.book_id WHERE books.in_stock= 'y';

或者

SELECT book_categories.book_id, all_categories.category FROM book_category 
JOIN   all_categories on book_categories.cat_id=all_categories.cat_id  
WHERE book_id IN   (SELECT book_id FROM books WHERE books.in_stock= 'y');