Question

I am working on following sql and keeping getting error on date part

Error i am getting is :- ORA-01861: literal does not match format string

  SELECT COUNT(*) 
  FROM  STGDBA.INTERACTIONS
  WHERE APP_ID='Home Depot'
  AND PEGA_ID ='0'
  AND TO_CHAR(to_date(END_TIME))BETWEEN TO_DATE('2012-AUG-01', 'YYYY-MON-DD')AND TO_DATE
('2012-AUG-31', 'YYYY-MON-DD')

This is how date is stored in database:- 2011-10-24 08:46:31.621

Answer 1

First off, you should never store date or timestamp data in a table using a VARCHAR2 data type. You should always use the proper data type (date, timestamp, timestamp with time zone, etc.). Storing data in the wrong data type leads to performance problems (the optimizer’s cardinality estimates are generally going to be much less accurate and indexing the column becomes much more problematic) as well as bugs that are difficult to find when some application inadvertently stores a string with the wrong format in your table causing various queries to start throwing errors or when subtle changes in execution plans cause errors to suddenly start (or stop) appearing.

Second, assuming every end_time string in every row in the table (whether or not the other two predicates are satisfied) is of the format YYYY-MM-DD HH24:MI:SS.FFF

SELECT COUNT(*) 
  FROM  STGDBA.INTERACTIONS
  WHERE APP_ID='Home Depot'
  AND PEGA_ID ='0'
  AND to_date(substr(END_TIME,1,length(end_time)-4), 
              'YYYY-MM-DD HH24:MI:SS' ) BETWEEN TO_DATE('2012-AUG-01', 'YYYY-MON-DD')
                                            AND TO_DATE('2012-AUG-31', 'YYYY-MON-DD')

You always want to compare dates to dates and strings to strings so you don’t want to wrap the left side of the expression with a to_char. You always want to specify an explicit format mask when you call to_date, which is what I do here. And a date does not have subsecond precision so you have to strip off the fractional seconds (this would not be an issue if you declared end_time to be a timestamp(3)).