Question

我正在尝试运行此查询：

delete FROM `customer` where customer_id 
not in (SELECT distinct customer_id FROM `order`);

但这需要很长时间，因为customer表有超过一百万条记录，因此会导致暂停和中断。

我怎样才能让它快速？任何替代方案？

修改的

以下是与SELECT相同的EXPLAIN：

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   PRIMARY     customer    index   NULL    PRIMARY     4   NULL    127659  Using where; Using index
2   DEPENDENT SUBQUERY  order   ALL     NULL    NULL    NULL    NULL    25141   Using where

Answer 1

尝试：

DELETE customer FROM customer t1 LEFT JOIN `order` t2 on t1.customer_id = t2.customer_id WHERE t2.customer_id is null;

Answer 2

首先，您可以从此DELETE命令中删除DISTINCT。这里没有必要。所以试试这个

delete FROM `customer` where customer_id 
not in (SELECT customer_id FROM `order`);

第二，请使用此重建查询检查执行计划

SELECT customer_id FROM `customer` where customer_id 
not in (SELECT customer_id FROM `order`);

这将显示MySQL如何执行此查询以及发生了什么。

如何优化此删除查询？

2 个答案: