hive 表中时间格式问题

1.有些数据格式存在着像‘2018.01.02’，把格式转化为‘2018-01-02’；

insert overwrite  table data3  select movies, to_date( from_unixtime(unix_timestamp(time_start,'yyyy.MM.dd'))),to_date(from_unixtime(unix_timestamp(time_end,'yyyy.MM.dd'))),company,director,actor,film_classification,piaofang,city from data1;