Calculating days of therapy in a sql query - sql

Question

I'm attempting to calculate days of therapy by month from an oracle database. The (vastly simplified) data is as follows:
Therapies
+-----------+-----------+----------+
| Rx Number | StartDate | StopDate |
|-----------+-----------+----------|
| 1 | 12-29-14 | 1-10-15 |
| 2 | 1-2-15 | 1-14-15 |
| 3 | 1-29-15 | 2-15-15 |
+-----------+-----------+----------+
For the purposes of this example, all times are assumed to be midnight. The total days of therapy in this table is (10-1 + 32-29) + (14-2) + (15-1 + 32-29) = 41. The total days of therapy in January in this table is (10-1) + (14-2) + (32-29) = 24.
If I wanted to calculate days of therapy for the month of January , my best effort is the following query:
SELECT SUM(stopdate - startdate)
FROM therapies
WHERE startdate > to_date('01-JAN-15')
AND stopdate < to_date ('01-FEB-15');
However, rx's 1 and 3 are not captured at all. I could try the following instead:
SELECT SUM(stopdate - startdate)
FROM therapies
WHERE stopdate > to_date('01-JAN-15')
AND startdate < to_date ('01-FEB-15');
But that would include the full duration of the first and third therapies, not just the portion in January. To make the matter more complex, I need these monthly summaries over a period of two years. So my questions are:
How do I include overhanging therapies such that only the portion within the target time period is included, and
How do I automatically generate these monthly summaries over a two year period?

Answer 1

How do I include overhanging therapies such that only the portion
within the target time period is included?
select sum(
greatest(least(stopdate, date '2015-01-31' + 1)
- greatest(startdate, date '2015-01-01'), 0)) suma
from therapies
How do I automatically generate these monthly summaries over a two
year period?
with period as (select date '2014-01-01' d1, date '2015-12-31' d2 from dual),
months as (select trunc(add_months(d1, level-1), 'Month') dt
from period connect by add_months(d1, level-1)<d2)
select to_char(dt, 'yyyy-mm') mth,
sum(greatest(least(stopdate, add_months(dt, 1)) - greatest(startdate, dt), 0)) suma
from therapies, months
group by to_char(dt, 'yyyy-mm') order by mth
Above queries produced desired output. Please insert your dates in proper places to change analyzed periods.
In second SQL inner subquery months gives 24 dates, one for each month. The rest is only maneuvering
with functions greatest(),least() and some math.

Answer 2

Use a case statement to set the start date and stop date. Like the below:
select sum(
Stopdate -
(case Startdate
when startdate < to_date(#YourBeginingDate) then To_date(#YourBeginingDate)
else startdate
end)
FROM therapies
WHERE stopdate > to_date(#YourBeginingDate)
AND StartDate < to_date(#YourEndingDate)

Answer 3

I would do something like the following:
WITH t1 AS (
SELECT 1 AS rx, DATE'2014-12-29' AS start_date
, DATE'2015-01-10' AS stop_date
FROM dual
UNION ALL
SELECT 2, DATE'2015-01-02', DATE'2015-01-14'
FROM dual
UNION ALL
SELECT 3, DATE'2015-01-29', DATE'2015-02-15'
FROM dual
)
SELECT TRUNC(rx_dt, 'MONTH') AS rx_month, SUM(rx_cnt) AS rx_day_cnt
FROM (
SELECT rx_dt, COUNT(*) AS rx_cnt
FROM (
SELECT rx, start_date + LEVEL - 1 AS rx_dt
FROM t1
CONNECT BY start_date + LEVEL - 1 < stop_date
AND PRIOR rx = rx
AND PRIOR DBMS_RANDOM.VALUE IS NOT NULL
) GROUP BY rx_dt
) GROUP BY TRUNC(rx_dt, 'MONTH')
ORDER BY rx_month
Results:
12/1/2014 12:00:00 AM 2
1/1/2015 12:00:00 AM 24
2/1/2015 12:00:00 AM 15
See SQL Fiddle here.
What I am doing is using LEVEL and CONNECT BY to get all the days of therapy based on start_date and stop_date (not inclusive). I then GROUP BY the therapy date (rx_dt) to handle the overlapping therapies. Then I GROUP BY the month of the therapy using the TRUNC() function.
This should work just fine over a two-year period (or more); just add that filter before the last GROUP BY:
WHERE rx_dt >= DATE'2014-01-01'
AND rx_dt < DATE'2016-01-01'
GROUP BY TRUNC(rx_dt, 'MONTH')
Note that if your primary key is composite, you should include all the columns in the CONNECT BY clause:
CONNECT BY start_date + LEVEL - 1 < stop_date
AND PRIOR rx = rx
AND PRIOR patient_id = patient_id
--etc.

Answer 4

This is a bit tricky, as you need to capture days from sessions that:
Begin before the month and end after the month
Begin before the month and end during the month
Begin during the month and end after the month
Begin during the month and end during the month
To get those sessions, you can use a WHERE statement like this (the # symbol means that those are variables being passed in):
*examples are in TSQL, PLSQL might have somewhat different syntax
WHERE startdate < #endDate AND stopdate > #startDate
That should capture all four of those scenarios that I listed.
Then you only need to capture days that occurred during the month. I do this with a query that replaces the startdate/enddate with the date range limits if they exceed the range, like this:
SELECT
CASE WHEN enddate > #endDate then #endDate ELSE enddate END -
CASE WHEN startdate < #startDate THEN #startDate ELSE startdate END
So your whole query should look like this:
SELECT
SUM(
CASE WHEN enddate > #endDate then #endDate ELSE enddate END -
CASE WHEN startdate < #startDate THEN #startDate ELSE startdate END
)
FROM therapies
WHERE startdate < #endDate AND stopdate > #startDate
If you want to run that for two years, toss that code in a function that accepts #startDate and #endDate parameters, then call it from a query that gives you two years worth of months, like this:
WITH dateCTE AS (
SELECT
GETDATE() AS StartDate,
DATEADD(Month, 1, GETDATE()) AS EndDate
UNION ALL
SELECT
DATEADD(MONTH, -1, StartDate),
DATEADD(MONTH, -1, EndDate)
FROM dateCTE
WHERE StartDate > DATEADD(YEAR, -2, GETDATE())
)
SELECT
StartDate,
EndDate,
SomeFunction(StartDate, EndDate)
FROM dateCTE