SELECT TO_CHAR(SYSDATE,'YYYY') AS YEAR FROM DUAL--查询当前年份

SELECT TO_CHAR(SYSDATE,'YYY') AS YEAR FROM DUAL--查询当前年份后两位

SELECT TO_CHAR(SYSDATE,'YY') AS YEAR FROM DUAL--查询当前年份最后两位

SELECT TO_CHAR(SYSDATE,'Y') AS YEAR FROM DUAL--查询当前年份最后一位

SELECT TO_CHAR(SYSDATE,'DDD') AS DAYS FROM DUAL

SELECT TO_CHAR(SYSDATE,'DD') AS DAYS FROM DUAL

SELECT TO_CHAR(SYSDATE,'dy') AS WEEK FROM DUAL

SELECT TO_CHAR(SYSDATE,'day') AS WEEK FROM DUAL 

SELECT TO_CHAR(SYSDATE,'DDD') AS DAYS FROM DUAL

SELECT TO_CHAR(SYSDATE,'Q') AS JD FROM DUAL

SELECT TO_CHAR(SYSDATE,'IW') AS WEEKNUM FROM DUAL

SELECT TO_CHAR(SYSDATE,'WW') AS WEEKNUM FROM DUAL

SELECT TO_CHAR(SYSDATE,'W') AS WEEKNUM FROM DUAL

SELECT TO_CHAR(last_day(to_date('2019/02/01','YYYY/MM/DD')),'DD') AS MONTH_DAYS_NUMBER FROM DUAL

SELECT TO_CHAR(SYSDATE,'YYYY/MM/DD') AS MONTH FROM DUAL--获取当前日期的'YYYY/MM/DD'格式：2020/01/02

SELECT TO_CHAR(SYSDATE,'YYYYMMDD') AS MONTH FROM DUAL--获取当前日期的'YYYYMMDD'格式：20200102

SELECT TO_CHAR(SYSDATE,'YYYYMMDD HH:MI:SS') AS now FROM DUAL--获取当前时间，精确到秒的12小时制格式：20200102 03:18:25

SELECT TO_CHAR(SYSDATE,'YYYYMMDD HH24:MI:SS') AS now FROM DUAL--获取当前时间，精确到秒24小时制的格式：20200102 15:18:13

SELECT TO_CHAR(SYSDATE,'YYYY/MM/DD HH24:MI:SS:PM:DY') AS now FROM DUAL--获取当前时间的格式，显示上、下午和星期几：2020/01/02 15:17:59:下午：星期四

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL '' second,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7秒前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL '' minute,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7分钟前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL ''hour ,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7小时前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL ''day ,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7天前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL ''month ,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7月前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - INTERVAL ''year ,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间的7年前时间

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS') AS NOW,TO_CHAR(SYSDATE - 8*INTERVAL ''hour ,'YYYY/MM/DD HH24:MI:SS') AS PAST FROM DUAL --查询当前时间参数年、月、日、时、分、秒乘以一个数字倍数之前的时间