Difficult time period calculations

Question

I have a monthly report where I have to add up periods of time between different records, without counting any overlapping time twice. Each record has its own start and stop date/time. The length of time from each record's start to its stop can be anything from 1 minute to the entire month. So for example, if there was 1 record that covered the whole month, I wouldn't need to look at any other records, because the whole month is covered. But if not, then I have all these pieces of time covering various parts of the month, some overlapping, some not.
If A starts at 1/1/01 0800 and
stops at 1/1/01 1200, and
B starts at 1/1/01 0900 and
stops at 1/1/01 1300, then I want to see the combination of these 2 as 5 hours. Other records C, D, ... could be entirely within this time period, or completely disjoint, or partially overlapping it. Again, I can't count any overlapping time twice. I have some lengthy code that does the job, but it takes a long time to run, because I create temp records that reflect the time periods found so far, and I don't add any new temp records that overlap the ones already created. It takes a long time to do all the comparisons. Anybody have any clever ideas for doing this faster?

Answer 1

Mike,
I believe this should work for you:
DECLARE
CURSOR c1 IS
SELECT start_date, end_date
FROM test_table
ORDER BY start_date;
v_total_time NUMBER := 0;
v_start_date DATE;
v_end_date DATE;
BEGIN
FOR r1 IN c1 LOOP
IF r1.start_date > NVL (v_end_date, r1.start_date - 1) THEN
v_start_date := r1.start_date;
ELSIF r1.end_date > v_end_date THEN
v_start_date := v_end_date;
END IF;
IF v_start_date IS NOT NULL THEN
v_total_time := v_total_time + (r1.end_date - v_start_date);
v_start_date := NULL;
v_end_date := r1.end_date;
END IF;
END LOOP;
DBMS_OUTPUT.put_line ('Total time: ' | | TO_CHAR (v_total_time) | | ' Days.');
END;
/