set schema lyma;
SELECT TO_CHAR(LAST_DAY(SYSDATE), 'yyyy-mm-dd') FROM lyma.DUAL; --本月最后一天
SELECT TO_CHAR(LAST_DAY(ADD_MONTHS(SYSDATE, -1)), 'yyyy-mm-dd') FROM lyma.dual; --上月最后一天
SELECT TO_CHAR(LAST_DAY(ADD_MONTHS(SYSDATE, -1)), 'yyyy-mm')||'-01' FROM lyma.dual; --上月第一天
--推荐下面的方法
SELECT TRUNC(CURRENT DATE,'MM') FROM DUAL; --本月最后一天
SELECT TRUNC(CURRENT DATE-1 MONTHS,'MM') FROM DUAL; --上月最后一天
SELECT (TRUNC(CURRENT DATE,'MM') - 1 days) FROM DUAL; --上月第一天