mysql - MySQL 查询重新设计

Question

我有以下查询从notes表中选择输入（例如：bob）不在orders表中的所有内容。

SELECT * FROM `notes` WHERE notes.customer_email NOT IN 
(SELECT customers_email_address FROM orders) 
AND ((customer_phone LIKE '%bob%') 
OR (customer_name LIKE '%bob%') 
OR (customer_email LIKE '%bob%')) 
AND customers_id IS NULL 
GROUP BY `customer_email` 
ORDER BY `customer_name` 
DESC LIMIT 50

这个查询的胖男孩在我的开发机器上花费了大约 80 秒，在实时服务器上花费了大约 7 秒。

两个问题：

1. 我对这个查询做错了什么？（我需要从错误中吸取教训）
2. 如何改进此查询？

Answer 1

尝试使用连接：

SELECT *
FROM
  `notes` left join orders
   on notes.customer_email=orders.customers_email_address
WHERE
  orders.customers_email_address is null
  AND notes.customers_id IS NULL 
  AND ((customer_phone LIKE '%bob%') 
        OR (customer_name LIKE '%bob%') 
        OR (customer_email LIKE '%bob%')) 
ORDER BY `customer_name` 
DESC LIMIT 50

它们通常比 IN/NOT IN 子句快。而且，我不知道你为什么在这里放一个 group by 子句。