mysql - 优化 MySQL 查询删除子查询

Question

有这些表:

customers
---------------------
`id` smallint(5) unsigned NOT NULL auto_increment,
`name` varchar(100) collate utf8_unicode_ci default NOT NULL,
....

customers_subaccounts
-------------------------
`companies_id` mediumint(8) unsigned NOT NULL,
`customers_id` mediumint(8) unsigned NOT NULL,
`subaccount` int(10) unsigned NOT NULL

我需要获取为同一家公司分配了多个子账户的所有客户。

这是我得到的:

SELECT * FROM customers 
WHERE id IN 
    (SELECT customers_id 
     FROM customers_subaccounts
     GROUP BY customers_id, companies_id 
     HAVING COUNT(subaccount) > 1)

虽然这个查询太慢了。如果我将 DISTINCT 修饰符添加到子查询的 SELECT 中的 customers_id，它会更慢，最终会为整个查询检索相同的客户列表。也许没有子查询有更好的方法，任何更快的方法都会有所帮助，我不确定它是否会检索到准确的正确列表。

有什么帮助吗？

Answer 1

您可以用 INNER JOIN 替换子查询:

SELECT t1.id
FROM customers t1
INNER JOIN
(
    SELECT DISTINCT customers_id 
    FROM customers_subaccounts
    GROUP BY customers_id, companies_id 
    HAVING COUNT(*) > 1
) t2
    ON t1.id = t2.customers_id