有一朋友现在遇到一个问题，有一目录存放的是图片文件，目录结构为三层，/uploads/avator/140320/*.jpg
也就是avator目录下有很多以目期命名的子目录，大概几百了。整个avator目录大概有8W左右的文件，其中有一部分文件
是无用了的垃圾文件，他想清掉。
这个目录中的大部分文件有一个表中的img_url字段记录了完全路径，即 路径+文件名, 比如：/upload/avator/140320/bid001.jpg。
他现在的作法是，遍历目录拿到所有文件名，然后查表 select 查 img_url like '%K',如果返回记录数等于0，就把这个文件从目录中删除掉。
表中的记录数有6W多条。
等于说有2W左右的文件是可删除的。
但是从运行来看，遍历目录很快，但是like时太慢了。。有没有更好更快的办法呀。
img_url字段建了索引
回复讨论(解决方案)
既然表中存放有完整的路径，那为什么还 like 呢？直接 = 不就快些
读取目录 glob('/uploads/avator/*/*.jpg') 放到一个临时表中
用这个临时表左连接数据表，右表为 null 的就是该删除的文件
img的src=“”时， 会导致有些浏览器显示一个x。 所以是不推荐将img的src设置为空的，。比较好的方案是remove image这个元素节点。
%开头的like是不启用索引的，像斑竹说的直接=
要么换个角度，遍历数据库，将有用的图片剪切到一个新文件夹，然后你懂的
谢谢各位指点
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