Timestamp comparission error

Question

hi, i have a table that stores the value as timestamp. Now how to compare two values ? as the fraction of a second is also stored .
sales             salestime
0                 2009-11-30 11:20:26.0  
112008        2009-11-30 11:37:56.156 in the above example the 2nd record is stored later . but how to find out ?
if i do
TO_date(a.salestime) < TO_date(b.salestime)
then i get error
ORA-01861: literal does not match format string
if i do
TO_date(a.salestime,'yyyy-mm-dd hh24:mi:ss:ff' )< TO_date(b.salestime,'yyyy-mm-dd hh24:mi:ss:ff')
then i get error
ORA-01821: date format not recognized
and if i do
TO_date(a.salestime,'yyyy-mm-dd hh24:mi:ss' )< TO_date(b.salestime,'yyyy-mm-dd hh24:mi:ss')
then i get error
ORA-01830: date format picture ends before converting entire input string
please help
thanks

Answer 1

Hi,
The DATE datatype does not include fractions of a second, so don't use DATEs. TO_DATE, as the name implies, returns a DATE.
The TIMESTAMP datatype does allow fractions of a second. Use TIMESTAMPs to store and compare dates with fractions of a second. There is a TO_TIMESTAMP function that is similar to TO_DATE, but it returns a TIMESTAMP.
Whatever you do, don't use VARCHAR2 columns to store dates.