Oracle: how to add minutes to a timestamp?

All of the other answers are basically right but I don't think anyone's directly answered your original question.

Assuming that "date_and_time" in your example is a column with type DATE or TIMESTAMP, I think you just need to change this:

to_char(date_and_time + (.000694 * 31))

to this:

to_char(date_and_time + (.000694 * 31), 'DD-MON-YYYY HH24:MI')

It sounds like your default date format uses the "HH" code for the hour, not "HH24".

Also, I think your constant term is both confusing and imprecise. I guess what you did is calculate that (.000694) is about the value of a minute, and you are multiplying it by the number of minutes you want to add (31 in the example, although you said 30 in the text).

I would also start with a day and divide it into the units you want within your code. In this case, (1/48) would be 30 minutes; or if you wanted to break it up for clarity, you could write ( (1/24) * (1/2) ).

This would avoid rounding errors (except for those inherent in floating point which should be meaningless here) and is clearer, at least to me.

In addition to being able to add a number of days to a date, you can use interval data types assuming you are on Oracle 9i or later, which can be somewhat easier to read,

SQL> ed
Wrote file afiedt.buf
SELECT sysdate, sysdate + interval '30' minute FROM dual
SQL> /

SYSDATE              SYSDATE+INTERVAL'30'
-------------------- --------------------
02-NOV-2008 16:21:40 02-NOV-2008 16:51:40