減少內部連接

Question

我有以下SQL-選擇（SQLite的/ MySQL的）：

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') 

有隻使用一個INNER JOIN的解決方案？問題是我想用兩個以上的spec-filter來製作SELECT。這可能嗎？

Answer 1

如果你想從規格表中均有記載那麼就不能簡化返回值，因爲兩個查找在你的榜樣的規格表所需

但是如下，你可以把它改寫：

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 

雖然我不認爲會有性能上的收益，除非你第一次做的規格表中查找，以找到匹配的product_id行，然後看着的名稱/值

Obviou狡猾的你需要索引規格表中的product_id，name和value字段，以及產品表中的productid，language和category字段。