Question

我有以下SQL-Select（SQLite / MySQL）：

SELECT products.* FROM products
INNER JOIN specifications AS spec1 ON specifications.product_id = product.id
INNER JOIN specifications AS spec2 ON specifications.product_id = product.id

WHERE products.language = "de"
AND products.category = "ABC"


AND (spec1.name = 'Innenabmessungen' AND spec1.value = '182x53')
AND (spec2.name = 'Farbe'            AND spec2.value = 'schwarz')

是否有仅使用一个INNER JOIN的解决方案？问题是我想使用两个以上的spec-filter制作SELECT s。这可能吗？

Answer 1

如果要从规范表中的两个记录返回值，则无法简化，因为规范表上需要两次查找

但是在您的示例中，您可以按如下方式重写它：

SELECT products.* FROM products

WHERE products.language = "de"
AND products.category = "ABC"
AND (SELECT COUNT(*) FROM specifications WHERE 
(specifications.name = 'Innenabmessungen' AND specifications.value = '182x53' AND specifications.product_id = product.id) OR
(specifications.name = 'Farbe' AND specifications.value = 'schwarz' AND specifications.product_id = product.id)
) = 2

虽然我认为性能不会有所提高，除非您首先在规范表上查找以找到具有匹配product_id的行，然后查找名称/值

显然，您需要索引规范表中的product_id，name和value字段，以及products表中的productid，language和category字段。

减少内部联接

1 个答案: