Mike Ault's thoughts on various topics, Oracle related and not. Note: I reserve the right to delete comments that are not contributing to the overall theme of the BLOG or are insulting or demeaning to anyone. The posts on this blog are provided “as is” with no warranties and confer no rights. The opinions expressed on this site are mine and mine alone, and do not necessarily represent those of my employer.

Wednesday, July 05, 2006

Oracle Timestamp Math

Had in interesting query from a client today. They have been storing start and stop times from a process in Oracle TIMESTAMP format and now want to get milliseconds out of the difference between the two timestamps. Seems pretty easy right?

Ok, first we create a table with two TIMESTAMP columns and an index value:

SQL> select * from check_time
SQL> /

---------------------------- ---------------------------- ----------
05-JUL-06 PM 05-JUL-06 PM 1
05-JUL-06 PM 05-JUL-06 PM 2

Now, if we were just using DATE we could subtract the dates and use the proper multiplier to convert the fractional return to the proper time unit. However when we subtract TIMESTAMPs:

SQL> select tim_col2-tim_col1 from check_time;

+000000000 00:01:12.547000
+000000000 00:00:24.547000

We get a hideous time interval upon which you can’t do math:

SQL> select sum(tim_col2-tim_col1) from check_time;
select sum(tim_col2-tim_col1) from check_time
ERROR at line 1:
ORA-00932: inconsistent datatypes: expected NUMBER got INTERVAL

So what can be done?

In steps the new interval functions that allow extraction of timestamp components, such as DAY, HOUR, MINUTE and SECOND…but wait there is no MILLISECOND! Of course a short trip to the documentation shows that the SECOND has a fractional component that allows us to specify the number of decimals after the second thus giving us access to the milliseconds, even down to microseconds in the interval value, look here:

SQL> l
1* select sum(extract(second from tim_col2)-extract(second from tim_col1))*1000 from check_time
SQL> /

Well, that is more like it! So now we can get the milliseconds between and do the aggregation functions such as sum() and avg() on the results.


Jeffermc said...

This is great, except, if the number of seconds is greater than 60, then you need to worry about the minutes, i.e. you'll not get a value of 60 or greater from EXTRACT(SECOND ...). You'll need to add 60*EXTRACT(MINUTE ...) in this case. And so on.

dink said...

thanx for the tip on timestamp/interval math. just made a function basing on this:

function get_seconds_from_interval(i_intrvl interval day to second) return number is
number of seconds & milliseconds (as a fractional part) encoded in interval variable
return extract(day from i_intrvl) * 86400 + extract(hour from i_intrvl) * 3600 + extract(minute from i_intrvl) * 60 + extract(second from i_intrvl);
when others then begin return null; end;