DB2获取第一天

 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