求一年中所有星期五的日期

思路：首先求出一年中的第一天和最后一天，然后枚举出一年的日历，最后筛选出星期5的日期即可

-- 求出一年中的第一天和最后一天（这里是第二年的第一天，-1得到最后天）

SQL> select trunc(sysdate,'y') first_day, add_months(trunc(sysdate,'y'),12) last_day from dual;
FIRST_DAY  LAST_DAY
---------- ----------
2014-01-01 2015-01-01

 

-- 求出一年有多少天

SQL> select add_months(trunc(sysdate,'y'),12)-trunc(sysdate,'y') num_days from dual;
NUM_DAYS
----------
365

 

-- 枚举日期

SQL> select trunc(sysdate, 'y') + level - 1 tdate
from dual
connect by level <= add_months(trunc(sysdate, 'y'), 12) - trunc(sysdate, 'y'))
TDATE
----------
2014-01-01
2014-01-02
2014-01-03
2014-01-04
...
...
2014-12-27
2014-12-28
2014-12-29
2014-12-30
2014-12-31

 

-- 求星期

SQL> select to_char(sysdate,'day') from dual;
TO_CHAR(SYSDATE,'DAY')
------------------------------------
thursday
SQL> select to_char(sysdate,'d') from dual;
T
-
5
这里注意
1 表示星期天
2 表示星期一
3 表示星期二
4 表示星期三
5 表示星期四
6 表示星期五
7 表示星期六

 

-- 求最后结果

SQL> with x as
2   (select trunc(sysdate, 'y') + level - 1 tdate
3      from dual
4    connect by level <=
5               add_months(trunc(sysdate, 'y'), 12) - trunc(sysdate, 'y'))
6  select tdate, to_char(tdate, 'day') from x where to_char(tdate, 'd') = 6
7  ;
TDATE      TO_CHAR(TDATE,'DAY')
---------- ------------------------------------
2014-01-03 friday
2014-01-10 friday
2014-01-17 friday
2014-01-24 friday
2014-01-31 friday
2014-02-07 friday
2014-02-14 friday
2014-02-21 friday
2014-02-28 friday
2014-03-07 friday
2014-03-14 friday
2014-03-21 friday
2014-03-28 friday
2014-04-04 friday
2014-04-11 friday
2014-04-18 friday
2014-04-25 friday
2014-05-02 friday
2014-05-09 friday
2014-05-16 friday
2014-05-23 friday
2014-05-30 friday
2014-06-06 friday
2014-06-13 friday
2014-06-20 friday
2014-06-27 friday
2014-07-04 friday
2014-07-11 friday
2014-07-18 friday
2014-07-25 friday
2014-08-01 friday
2014-08-08 friday
2014-08-15 friday
2014-08-22 friday
2014-08-29 friday
2014-09-05 friday
2014-09-12 friday
2014-09-19 friday
2014-09-26 friday
2014-10-03 friday
2014-10-10 friday
2014-10-17 friday
2014-10-24 friday
2014-10-31 friday
2014-11-07 friday
2014-11-14 friday
2014-11-21 friday
2014-11-28 friday
2014-12-05 friday
2014-12-12 friday
2014-12-19 friday
2014-12-26 friday
52 rows selected.

 

--求当月的第一个星期一和最后一个星期一

SQL> select next_day(trunc(sysdate,'mm')-1,2),next_day(last_day(trunc(sysdate,'mm'))-7,2) from dual;
NEXT_DAY(T NEXT_DAY(L
---------- ----------
2014-01-06 2014-01-27