我尝试列出特定图书作者所有的书籍销售信息。所以我有一个查询,但它没有使用索引来查找记录。
以下是我的表结构:
以下是我的表结构:
-- Table structure for table `books`
CREATE TABLE IF NOT EXISTS `books` (
`book_id` int(11) NOT NULL auto_increment,
`author_id` int(11) unsigned NOT NULL,
`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`),
KEY `author_id` (`author_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
-- Dumping data for table `books`
INSERT INTO `books` (`book_id`, `author_id`, `book_type_id`, `book_title`, `book_price`, `in_stock`) VALUES
(1, 1, 1, 'My Book 1', 10, 'y'),
(2, 2, 1, 'My Book 2', 20, 'n'),
(3, 1, 2, 'My Book 3', 30, 'y'),
(4, 3, 3, 'My Book 4', 40, 'y'),
(5, 4, 2, 'My Book 5', 50, 'n'),
(6, 1, 1, 'My Book 6', 60, 'y'),
(7, 5, 3, 'My Book 7', 70, 'n'),
(8, 6, 2, 'My Book 8', 80, 'n'),
(9, 7, 1, 'My Book 9', 90, 'y'),
(10, 8, 3, 'My Book 10', 100, 'n');
-- Table structure for table `book_sales`
CREATE TABLE IF NOT EXISTS `book_sales` (
`sale_id` int(11) NOT NULL auto_increment,
`book_id` int(11) NOT NULL,
`sale_amount` decimal(8,2) NOT NULL default '0.00',
`time` datetime NOT NULL default '0000-00-00 00:00:00',
`price` smallint(8) NOT NULL,
PRIMARY KEY (`sale_id`),
KEY `book_id` (`book_id`),
KEY `price` (`price`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
-- Dumping data for table `book_sales`
INSERT INTO `book_sales` (`sale_id`, `book_id`, `sale_amount`, `time`, `price`) VALUES
(1, 1, '10.00', '2010-02-23 10:00:00', 20),
(2, 1, '20.00', '2010-02-24 11:00:00', 20);
我的查询:
SELECT sale_amount, price
FROM book_sales
INNER JOIN books ON book_sales.book_id = books.book_id
WHERE books.author_id =1
对于上面的问题,使用EXPLAIN显示:
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE books ref PRIMARY,author_id author_id 4 const 3 Using index
1 SIMPLE book_sales ALL book_id NULL NULL NULL 2 Using where
显然,book_sales没有使用我拥有的索引'book_id'。我该怎么做才能让book_sales表使用这个索引呢?
谢谢。
根据建议进行了编辑(但结果仍然没有使用索引):
//Does not use the index in book_sales table
EXPLAIN SELECT sale_amount, price
FROM books, book_sales
FORCE INDEX ( book_id )
WHERE book_sales.book_id = books.book_id
AND books.author_id =1
//Does not use the index in book_sales table
EXPLAIN SELECT sale_amount, price
FROM book_sales, books
WHERE books.author_id = 1
AND book_sales.book_id = books.book_id
如何强制让只有两行的book_sale表使用索引?谢谢。