I have an application that is used by users across the country. It reads
from a table in a centrally located database. It needs to convert a
standard date in the table to the timezone of the user.

I initially wrote a function, TO_STZ to convert a date to the
sessiontimezone:

RETURN
arg_date(+(to_number(substr(dbtimezone,2,2))-to_number(substr(sessiontimezone,2,2)/24

when the user issues the statement SELECT TO_STZ(date_field) from TABLE
the date in the table was converted.

This worked fine up until Daylight Saving Time - at which point sessiontime
changed by -1 hour but dbtimezone stayed the same (I didn't realize at the
time that it was a constant offset from GMT)

Any suggestions on a function that does what I want?

Thanks, Marty