oracle日期的相关有用统计SQL

1、求某个月有多少天

SQL> select sysdate,to_number(to_char(last_day(sysdate),'DD')) from dual;

SYSDATE   TO_NUMBER(TO_CHAR(LAST_DAY(SYSDATE),'DD'))
--------- ------------------------------------------
28-JUN-19					  30

2、计算一个月还剩多少天

SQL> select sysdate,last_day(sysdate)-sysdate from dual;

SYSDATE   LAST_DAY(SYSDATE)-SYSDATE
--------- -------------------------
28-JUN-19			  2

3、今天是星期几

SQL> select to_char(sysdate,'DAY') from dual;

TO_CHAR(SYSDATE,'DAY')
------------------------------------
FRIDAY

4、今天是几号

SQL> select extract(DAY from sysdate) from dual;

EXTRACT(DAYFROMSYSDATE)
-----------------------
		     28

5、今天是一年的第几天

SQL> select to_char(sysdate,'DDD') from dual;

TO_
---
179