優化MySQL的NOT IN查詢

Question

我這是基於以下SQL查詢產生的下拉列表：

SELECT * FROM product WHERE 
    product.id NOT IN (SELECT customer_1.product_id FROM customer_1 WHERE (customer_1.product_id != '$x')) 
AND product.id NOT IN (SELECT customer_2.product_id FROM customer_2 WHERE (customer_2.product_id != '$x')) 
AND product.id NOT IN (SELECT customer_3.product_id FROM customer_3 WHERE (customer_3.product_id != '$x')); 

即就出現在這裏是執行時間的問題。這個查詢本身大約需要5.3秒。我在同一頁面上有幾個其他類似的查詢。

我的問題是：是否有實現相同結果的更好，更快的方式？

預先感謝您。

Answer 1

您可能會從LEFT JOIN s獲得更好的性能，在連接的右側（customer_*表）查找NULL。如果我明白你的目標，這應該做的工作：

SELECT 
    products.* 
FROM 
    products 
    LEFT JOIN customer_1 ON products.id = customer_1.product_id 
    LEFT JOIN customer_2 ON products.id = customer_2.product_id 
    LEFT JOIN customer_3 ON products.id = customer_3.product_id 
WHERE 
    products.id != '$x' 
    AND customer_1.product_id IS NULL 
    AND customer_2.product_id IS NULL 
    AND customer_3.product_id IS NULL 

Answer 2

你應該使用NOT EXISTS。有了正確的索引表，這種情況下它可以顯著更快。

Answer 3

SELECT * FROM product Left join (SELECT customer_1.product_id FROM customer_1 WHERE (customer_1.product_id != '$x')) as t1 Left join (SELECT customer_2.product_id FROM customer_2 WHERE (customer_2.product_id != '$x')) as t2 left join (SELECT customer_3.product_id FROM customer_3 WHERE customer_3.product_id != '$x')) as t3 
And t3.product_id is null and t1.product_id is null and t2.product_id is null