python - 如何使用连接删除mysql行

Question

c2.execute("delete from entity_map where canon_id in (select canon_id from
entity_map_session where canon_id in (select canon_id from 
entity_map_session group by canon_id having count(canon_id) < 10))")

我想加快上面这组操作的速度。特别是我们删除行的最后一个。最好的方法是什么？

Answer 1

针对 entity_map_session2 表的子查询正在执行计数聚合，并且没有 WHERE 或 HAVING 子句，这意味着它不能优化了很多。但是，您可以删除不必要的嵌套子查询之一，例如使用:

DELETE
FROM entity_map2
WHERE canon_id IN (SELECT canon_id FROM entity_map_session2
                   GROUP BY canon_id HAVING COUNT(canon_id) < 10);