How to convert a postgres database from CST to GMT? - postgresql

Question

I setup a postgres db that was installed on a server in the Central Time Zone so all the timestamp columns are in Central Time Zone.
Is there a way in postgres to change all the timezone columns in a database from CST to GMT? Is it a best practice to configure databases to use GMT?

Answer 1

Well, best practice is to avoid using TIMESTAMP type which does not know anything about timezones and to always use TIMESTAMPTZ (short for TIMESTAMP WITH TIME ZONE) type to store your timestamps.
TIMESTAMPTZ stores both timestamp in UTC and timezone in which timestamp was originally written to (like CST, PST or GMT+6). This allows you to always manipulate and display these columns correctly, no matter what current server or client timezone setting is.
You should be able to convert your existing TIMESTAMP columns into TIMESTAMPTZ using something like:
ALTER TABLE mytable ALTER COLUMN old_tstamp TYPE TIMESTAMPTZ
Before doing this, you should experiment on small dataset or maybe small test table on how conversion from TIMESTAMP to TIMESTAMPTZ is really working for you such that time zone information is preserved on your data.
If conversion does not work correctly, you can temporarily set timezone for current session (you need it only for conversion purposes) using statement like (use it before ALTER TABLE ... COLUMN ... TYPE):
SET timezone TO 'CST6CDT';
or
SET timezone TO 'UTC+6';
This will affect subsequent operations and conversions from TIMESTAMP to TIMESTAMPTZ - just make sure to get it right.
After you have converted all timestamps to TIMESTAMPTZ, server or client timezone setting (which defaults to current operating system timezone setting) is only useful for display purposes, as data manipulation will be always correct.