用SQL语句获取常见的几种日期

---上周
SELECT TO_CHAR(TRUNC(SYSDATE, 'IW') - 7, 'yyyymmdd') FROM DUAL
SELECT TO_CHAR(TRUNC(SYSDATE, 'IW') - 1, 'yyyymmdd') FROM DUAL

---本周
SELECT TO_CHAR(TRUNC(SYSDATE, 'IW') , 'yyyymmdd') FROM DUAL
SELECT TO_CHAR(TRUNC(SYSDATE, 'IW') + 6, 'yyyymmdd') FROM DUAL

---上一月的第一天和最后一天
select trunc(add_months(sysdate, -1), 'mm') first_day,
       last_day(add_months(sysdate, -1)) last_day
  from dual
---本月的最后一天
SELECT TO_CHAR(last_day(add_months(sysdate, 0)), 'yyyymmdd') FROM DUAL

---当年 第一天
SELECT TO_CHAR(trunc(sysdate, 'yyyy'), 'yyyymmdd') FROM DUAL
---上年最后一天
SELECT TO_CHAR(trunc(sysdate,'iyyy'), 'yyyymmdd') FROM DUAL

---当月第一天
SELECT TO_CHAR(trunc(sysdate,'mm'), 'yyyymmdd') FROM DUAL
---当月数值
SELECT TO_CHAR(sysdate,'mm') FROM DUAL

---当周数值
SELECT TO_CHAR(sysdate,'ww') FROM DUAL