为什么走索引还需要消耗8秒,explain检查 这条扫描了30多万条
SELECT * FROM topic where pid=4 and status=1 and id<393203 order by id desc LIMIT 15
只要0.01秒
SELECT * FROM topic where pid=4 and status=1 order by id desc LIMIT 15
只要0.01秒
SELECT * FROM topic where status=1 and id<393203 order by id desc LIMIT 15
为什么where pid=4和id<393203 组合,就变慢了