date转为timstamp
date转为timstam可以函数to_timestamp的方式来转化：

SELECT to_timestamp('2018-06-19 12:10:10.1','yyyy-mm-dd hh24:mi:ss.ff')
FROM dual;

timestamp转化为date
1, timestamp+0
select Systimestamp+0 FROM DUAL;

2, to_char的方式
Select to_char(Systimestamp,'yyyymmdd') From dual;

3，cast转化
Select Cast(Systimestamp As Date) From dual;