How to calculate time duration using Microsoft SQL? - sql

Question

I want to find the time duration for each person from one start time. I want to calculate the time duration from 1 start time for each day and multiple end times for multiple users. This is my code:
SELECT *,
CAST(DATEDIFF(n, CAST(End_Time AS datetime),
CAST(Start_Time AS datetime)) AS FLOAT) / 60 AS Time_Duration
FROM
( SELECT NAME,
MAX(CASE WHEN DESCRIPTION = 'Green' THEN Final_Value END) AS Start_Time,
MAX(CASE WHEN DESCRIPTION = 'Red' THEN Final_Value END) AS End_Time
FROM mydata
WHERE NAME != ‘NA’
GROUP BY NAME
) C
I am not able to get any results for time duration.
This is what my output looks like:
Name Start_time End_time Time_Duration
1 Day_1 5/6/15 2:30
2 John 5/6/15 3:30
3 Ben 5/6/15 4:30
4 Mike 5/6/15 5:30
5 Day_2 5/7/15 2:30
6 John_2 5/7/15 4:30
7 Ben_2 5/7/15 5:30
8 Mike_2 5/7/15 6:30
I want it to look like this:
Name Start_time End_time Time_Duration
1 Day_1 5/6/15 2:30
2 John 5/6/15 3:30 1.00
3 Ben 5/6/15 4:30 2.00
4 Mike 5/6/15 5:30 3.00
5 Day_2 5/7/15 2:30
6 John_2 5/7/15 4:30 2.00
7 Ben_2 5/7/15 5:30 3.00
8 Mike_2 5/7/15 6:30 4.00

Answer 1

Assuming that the values in name column has suffix of the day number (and none for day 1)
WITH td AS
(
SELECT *,
ROW_NUMBER() OVER (PARTITION BY [day] ORDER BY final_value) rnum
FROM (SELECT *,
CASE WHEN CHARINDEX('_', name) = 0
THEN '1'
ELSE SUBSTRING(name, CHARINDEX('_', name) + 1, LEN(name) - CHARINDEX('_', name))
END [day]
FROM t_dur
) tt
)
SELECT t1.name,
CASE WHEN rnum = 1 THEN t1.final_value END start_time,
CASE WHEN rnum <> 1 THEN t1.final_value END end_time,
CASE CAST(DATEDIFF(hour, (SELECT t2.final_value FROM td t2 WHERE t2.[day] = t1.[day] AND t2.rnum = 1),
t1.final_value) AS DECIMAl(5,2))
WHEN 0 THEN NULL
ELSE CAST(DATEDIFF(hour, (SELECT t2.final_value FROM td t2 WHERE t2.[day] = t1.[day] AND t2.rnum = 1),
t1.final_value) AS DECIMAl(5,2))
END time_duration
FROM td t1
Result
name start_time end_time time_duration
Day_1 2015-05-06 02:30:00.000 NULL NULL
John NULL 2015-05-06 03:30:00.000 1.00
Ben NULL 2015-05-06 04:30:00.000 2.00
Mike NULL 2015-05-06 05:30:00.000 3.00
Day_2 2015-05-07 02:30:00.000 NULL NULL
John_2 NULL 2015-05-07 04:30:00.000 2.00
Ben_2 NULL 2015-05-07 05:30:00.000 3.00
Mike_2 NULL 2015-05-07 06:30:00.000 4.00