Date Comparison Error

Question

I have a database column named lastname this has text data entered in form of: 05/15/2010  and so on.  ---long story on why text field and not date....
My code is as follows:
select b.lastname as sale_date, c.combined_legal as legal_address
  from anthem_prod_usr.opr_logi_documents      a
  ,    anthem_prod_usr.opr_parties             b
  ,    anthem_prod_usr.opr_legal_headers       c
  ,    anthem_prod_usr.image_references        f
  ,    prod_pa.valid_dates                     g
where a.instrument_number = b.instrument_number
   and a.multi_seq = b.multi_seq
   and b.name_type = 'E'
   and b.lastname like ('__/__/____')
   and a.instrument_number = c.instrument_number
   and c.multi_seq = c.multi_seq
   and trunc(to_date(b.lastname,'mm/dd/yyyy')) between trunc(to_date('07/10/2010','mm/dd/yyyy')) and trunc(to_date('08/01/2010','mm/dd/yyyy'))
   and f.content_type_id = 'PUBLIC'
   and a.document_type = 'FORECLOSURE'
Error I receive is:
ORA-01843: not a valid month
01843. 00000 -  "not a valid month"
*Cause:   
*Action:
Using trunc function, I thought I was trimming time off to do only date comparison.  Not sure why this error occurs.

Answer 1

Hi,
This shows one of the many reasons why storing date information in VARCHAR2 columns is such a bad idea.
TRUNC is irrelevant here.  The error occurs in TO_DATE.  You're doing TRUNC on the results of TO_DATE, so nothing you do with TRUNC will affect the error.
You must have some bad data in the column.  If you can't actually clean up the table, then you have to detect the bad data before attempting TO_DATE.
Remember, the optimizer decides which conditions in the WHERE clause will be done first.  There's no guarantee that
and b.lastname like ('__/__/____')
will be applied before TO_DATE.  Even if it is, the condition above is just testing that the string is the right length and has slashes in the right places.  It's checking that (for example) the month is between '01' and '12', or even if the month is numbers.  The string '//////FOO/' meets the condition above.
See https://forums.oracle.com/message/4255051 for validating date information in SQL.
If you need help, post a complete test case that people can run to re-create the problem and test their ideas.  Include CREATE TABLE and INSERT statements for any tables needed. Also post the results you want from that sample data given.
Simplify the problem as much as possible.  Remove any tables or conditions or anything else that isn't related to the problem.
See the forum FAQ https://forums.oracle.com/message/9362002#9362002