SQL 计算一年有多少天

1  select 'Days in 2005: '||
2         to_char(add_months(trunc(sysdate,'y'),12)-1,'DDD')
3         as report
4    from dual
5  union all
6  select 'Days in 2004: '||
7         to_char(add_months(trunc(
8                      to_date('01-SEP-2004'),'y'),12)-1,'DDD')
9    from dual
　
REPORT
-----------------
Days in 2005: 365
Days in 2004: 366

select trunc(to_date('01-SEP-2004'),'y')
  from dual
　
TRUNC(TO_DA
-----------
01-JAN-2004

select add_months(
         trunc(to_date('01-SEP-2004'),'y'),
         12) before_subtraction,
       add_months(
         trunc(to_date('01-SEP-2004'),'y'),
         12)-1 after_subtraction
  from dual
　
BEFORE_SUBT AFTER_SUBTR
----------- -----------
01-JAN-2005 31-DEC-2004

select to_char(
         add_months(
           trunc(to_date('01-SEP-2004'),'y'),
           12)-1,'DDD') num_days_in_2004
  from dual
　
NUM
---
366