APEX

hi all,

i am facing problem with date column.

when i am trying to do execute a query this works fine

select null as link,'S'||to_char(DATE_OF_JOIN,'YY'),COUNT(STUDENT) "Blue Acres" from STUDENT_RECORD where PROCESSOR=1 and DATE_OF_JOIN >= to_date('0620' || to_char(sysdate, 'YYYY'), 'MMDDYYYY') and DATE_OF_JOIN < to_date('0920' || to_char(sysdate, 'YYYY'), 'MMDDYYYY') group by to_char(DATE_OF_JOIN,'YY')

and when i am trying the below query its showing the only this year dates its not referring the previous years

select null as link,'S'||to_char(DATE_OF_JOIN,'MMDDYY'),COUNT(STUDENT) "Blue Acres" from STUDENT_RECORD where PROCESSOR=1 and DATE_OF_JOIN >= to_date('1220' || to_char(sysdate, 'YYYY')-1, 'MMDDYYYY') and DATE_OF_JOIN < to_date('0320' || to_char(sysdate, 'YYYY'), 'MMDDYYYY') group by to_char(DATE_OF_JOIN,'MMDDYY')

when i am trying below query its showng the error ORA-01843: not a valid month

select null as link,'Fall'||to_char(to_char(DATE_OF_JOIN,'YY')-1),COUNT(STUDENT) "Blue Acres" from STUDENT_RECORD where PROCESSOR=1 and DATE_OF_JOIN >= to_date('0620' || to_char(sysdate, 'YYYY')-1, 'MMDDYYYY') and DATE_OF_JOIN < to_date('0920' || to_char(sysdate, 'YYYY')-1, 'MMDDYYYY') group by to_char(to_char(DATE_OF_JOIN,'YY')-1)


can any help me regarding the problem pls

Regards,
Pavan