1. 日期格式转化（参考）

select beg_time, end_time, extract(epoch from to_timestamp(end_time,’yyyy-mm-dd-HH24-MI-SS-US’))-extract(epoch from to_timestamp(beg_time,’yyyy-mm-dd-HH24-MI-SS-US’)) from cdb_all_iu_data where beg_time > ‘2017-09-21’