SQL查询不拉记录相同

Question

I have this query:

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`

which pulls up nothing. HOWEVER, if i do this query it finds the right record:

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

The strangest part though, other records it will work for. if I use the accession_number 0396, if finds the right record in both queries. I can't for the life of me figure out what is going on. Any help is greatly appreciated.

Answer 1

You need to use LEFT JOIN with matierial_types because it is possible that this table doesn't have the same materialType id of books try this

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

It looks like you have no entry in 'Book' that corresponds to an item with an 'accession_number' of 0936. A Right Join to Items should reveal this:

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`