Question

我有一个下拉列表，它是根据以下sql查询生成的：

 
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'));

这里出现的问题是执行时间。这个查询本身需要大约5.3秒。我在同一页面上有几个其他类似的查询。

我的问题是：是否有更好，更快的方法来实现相同的结果？

提前谢谢。

Answer 1

您可以从LEFT JOIN获得更好的性能，在联接的右侧查找NULL（customer_*表）。如果我了解你的目标，那就应该做好这个工作：

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

您应该使用NOT EXISTS。使用正确索引的表格，这种情况可以明显加快。

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

优化MySQL NOT IN查询

3 个答案: