ORACLE常用功能

-- 删除重复记录
DELETE from mytable t1 WHERE ROWID > (SELECT MIN (ROWID) from mytable t2 WHERE t1. key = t2.key);
-- 当前日期
SELECT TO_CHAR(SYSDATE, 'yyyy-MM-dd') from DUAL;
-- 上月当前日期
SELECT TO_CHAR(ADD_MONTHS(SYSDATE,
-1), 'yyyy-MM-dd') from DUAL;
-- 下月当前日期
SELECT
TO_CHAR(ADD_MONTHS(SYSDATE, 1), 'yyyy-MM-dd') from DUAL;
--
上月首天
SELECT TO_CHAR(ADD_MONTHS(LAST_DAY(SYSDATE) + 1,
-2),'yyyy-MM-dd') from DUAL;
-- 上月月末
SELECT
TO_CHAR(LAST_DAY(ADD_MONTHS(LAST_DAY(SYSDATE) + 1, -2)),'yyyy-MM-dd') from DUAL;
-- 当月首天
SELECT
TO_CHAR(ADD_MONTHS(LAST_DAY(SYSDATE) + 1, -1), 'yyyy-MM-dd') from DUAL;
-- 当月月末
SELECT
TO_CHAR(LAST_DAY(ADD_MONTHS(LAST_DAY(SYSDATE) + 1, -1)),'yyyy-MM-dd') from DUAL;
-- 下月首天
SELECT
TO_CHAR(ADD_MONTHS(LAST_DAY(SYSDATE) + 1, 0), 'yyyy-MM-dd') from DUAL;
-- 下月月末
SELECT
TO_CHAR(LAST_DAY(ADD_MONTHS(LAST_DAY(SYSDATE) + 1, 0)), 'yyyy-MM-dd') from DUAL;
-- 今年首天
SELECT TO_CHAR(TRUNC(SYSDATE,'Y'), 'yyyy-MM-dd') from DUAL;