select 1st and 15th of every month

select to_char(days, 'fmMon ddth'||' - '||'fmmm/dd/yyyy') days
    from
       (select sysdate + level as days
       from dual
        connect by level <= to_date ('09/30/2008', 'mm/dd/yyyy') - sysdate)
   where extract(day from days) in (1, 15)
   /

DAYS
---------------------
Jun 15th - 06/15/2008
Jul 1st - 07/01/2008
Jul 15th - 07/15/2008
Aug 1st - 08/01/2008
Aug 15th - 08/15/2008
Sep 1st - 09/01/2008
Sep 15th - 09/15/2008

SQL> SELECT TO_CHAR(TO_DATE('1900-01-01', 'YYYY-MM-dd'), 'dth')
  2    FROM DUAL
  3  /

TO_
---
2nd

SQL> select ADD_MONTHS(trunc(sysdate,'YEAR'),12)-1 from dual
  2  /

ADD_MONTH
---------
31-DEC-19

SQL> select trunc(to_date('18-sep-2006','dd-mon-yyyy'),'year') from dual;

TRUNC(TO_
---------
01-JAN-06

SQL> SELECT round(sysdate,'YYYY'),add_months(trunc(sysdate,'YYYY')-1,12) from dual
  2  /

ROUND(SYS ADD_MONTH
--------- ---------
01-JAN-20 31-DEC-19


There's an in-built SQL function to do this.

Function Name: TRUNC

SQL> SELECT TRUNC(TO_DATE('17-DEC-2001'),'YEAR') "First Day" FROM Dual;

First Day
---------
01-JAN-01

SQL> SELECT TRUNC(SysDate,'YEAR') "First Day" FROM Dual;

First Day
---------
01-JAN-02

https://www.viralpatel.net/useful-oracle-queries/