请问怎么讲2014-12-20 00:00:00.000变更为2014-12这种格式

Question

select to_char(systimestamp,'YYYY-MM') from dual;  
select to_char( TO_TIMESTAMP_TZ('2014-12-20 00:00:00.000','YYYY-MM-DD HH24:MI:SS.FF'),'YYYY-MM')from dual;

Answer 1

select substr('2014-12-20 00:00:00.000',1,7) from dual;

Answer 2

select to_char(to_timestamp('2014-12-20 00:00:00.000','yyyy-MM-DD HH24:mi:ss.ff'),'yyyy-mm') from dual

Answer 3

select to_char(sysdate,'yyyy-mm') from dual;