详见：http://blog.yemou.net/article/query/info/tytfjhfascvhzxcyt411
Stackowerflow 上关于这两个时间有人这样解释
Fetch time - measures how long transferring fetched results take, which has nothing to do with query execution. I would not consider it as sql query debugging/optimization option since fetch time depends on network connection, which itself does not have anything to do with query optimization. If fetch time is bottleneck then more likely there's some networking problem.
Note: fetch time may vary on each query execution.
Duration time - is the time that query needs to be executed. You should try to minimize it when optimizing performance of sql query.
其实说通俗一些，fetch time 就是数据在网络上传输花费的时间，duration time是sql真正执行的时间