请各位高手帮忙： 假如我有两张及字段如下： a topic_id ,topic_name .... b post_id ,topic_id.... 我的sql语句如下： sql=delete from a topic_id not in(select * from b) where topic_id=1; 这样对吗？我的意思是：删除a表，如果a表的id在b表中存在，就不删除，请各位高手指点！SQL code: delete from a where topic_id not in (select topic_id from b);
delete from a where topid_id not in (select topic_id from b) 或者如下也可以，速度上会有些差别。 SQL code: delte a from a left join b using(topic_id) where b.topic_id is null
或者 delete from a where not exists (select 1 from b where topic_id=a.topic_id); SQL code: delete from a where topic_id not in(select topic_id from b) and topic_id=1;
delete A from a LEFT JOIN B ON A.topic_id=B.topic_id where A.topic_id=1 AND b.topic_id is null delete from a where topic_id not in (select topic_id from b); 同意一楼！
