Question

我有这个问题：

SELECT Book.title, Book.copyright, Book.publisher, Book.id,
    MaterialType.type, Item.id as item_id, 100 as relevance FROM `books` AS `Book`
inner JOIN `material_types` AS `MaterialType` ON (`MaterialType`.`id` = `Book`.`material_type_id`)
inner JOIN `items` AS `Item` ON (`Item`.`book_id` = `Book`.`id` AND `Item`.`accession_number` = '0936')
WHERE 1 = 1  GROUP BY `Book`.`id`

什么都没有。但是，如果我执行此查询，它会找到正确的记录：

SELECT * FROM `items` AS `Item` WHERE `Item`.`accession_number` = '0936'

最奇怪的部分，它将起作用的其他记录。如果我使用accession_number 0396，如果在两个查询中找到正确的记录。我不能为我的生活弄清楚发生了什么。非常感谢任何帮助。

Answer 1

你需要使用LEFT JOIN和matierial_types，因为这个表可能没有相同的materialType id书籍试试这个

SELECT Book.title, Book.copyright, Book.publisher, Book.id,
    MaterialType.type, Item.id as item_id, 100 as relevance FROM `books` AS `Book`
LEFT JOIN `material_types` AS `MaterialType` ON (`MaterialType`.`id` = `Book`.`material_type_id`)
LEFT JOIN `items` AS `Item` ON (`Item`.`book_id` = `Book`.`id`) 
WHERE `Item`.`accession_number` = '0936'
GROUP BY `Book`.`id`

Answer 2

看起来你在'Book'中没有对应于'accession_number'为0936的项目的条目。正确加入项目应该揭示：

SELECT Book.title, Book.copyright, Book.publisher, Book.id,
    MaterialType.type, Item.id as item_id, 100 as relevance FROM `books` AS `Book`
left JOIN `material_types` AS `MaterialType` ON (`MaterialType`.`id` = `Book`.`material_type_id`)
right JOIN `items` AS `Item` ON (`Item`.`book_id` = `Book`.`id` AND `Item`.`accession_number` = '0936')
WHERE 1 = 1  GROUP BY `Book`.`id`

sql查询不拉记录相同

2 个答案: