Oracle, Make date time's first day of its month

According to http://psoug.org/reference/date_func.html, this should work a dandy...

SELECT TRUNC(yourDateField, 'MONTH') FROM yourTable

SQL> select to_date('31/07/2010', 'DD/MM/YYYY') from dual;

TO_DATE('
---------
31-JUL-10

SQL> select trunc(to_date('31/07/2010', 'DD/MM/YYYY'), 'MM') from dual;

TRUNC(TO_
---------
01-JUL-10

SQL>

select trunc(sysdate, 'mm') from dual;