Hive中yyyymmdd和yyyy-mm-dd日期之间的切换

方法1: from_unixtime+ unix_timestamp

--20171205转成2017-12-05 
select from_unixtime(unix_timestamp('20171205','yyyymmdd'),'yyyy-mm-dd') from dual;

--2017-12-05转成20171205
select from_unixtime(unix_timestamp('2017-12-05','yyyy-mm-dd'),'yyyymmdd') from dual;

方法2: substr + concat
--20171205转成2017-12-05 
select concat(substr('20171205',1,4),'-',substr('20171205',5,2),'-',substr('20171205',7,2)) from dual;

--2017-12-05转成20171205
select concat(substr('2017-12-05',1,4),substr('2017-12-05',6,2),substr('2017-12-05',9,2)) from dual;

方法3: split + concat_ws(concat不行)
--2019-01-03转成20190103
select concat_ws('',split('2019-01-03','-'));