SQL Server - Counting total number of days user had active contracts - sql

Question

I want to count the number of days while user had active contract based on table with start and end dates for each service contract. I want to count the time of any activity, no matter if the customer had 1 or 5 contracts active at same time.
+---------+-------------+------------+------------+
| USER_ID | CONTRACT_ID | START_DATE | END_DATE |
+---------+-------------+------------+------------+
| 1 | 14 | 18.02.2021 | 18.04.2022 |
| 1 | 13 | 02.01.2019 | 02.01.2020 |
| 1 | 12 | 01.01.2018 | 01.01.2019 |
| 1 | 11 | 13.02.2017 | 13.02.2019 |
| 2 | 23 | 19.06.2021 | 18.04.2022 |
| 2 | 22 | 01.07.2019 | 01.07.2020 |
| 2 | 21 | 19.01.2019 | 19.01.2020 |
+---------+-------------+------------+------------+
In result I want a table:
+---------+--------------------+
| USER_ID | DAYS_BEEING_ACTIVE |
+---------+--------------------+
| 1 | 1477 |
| 2 | 832 |
+---------+--------------------+
Where
1477 stands by 1053 (days from 13.02.2017 to 02.01.2020 - user had active contracts during this time) + 424 (days from 18.02.2021 to 18.04.2022)
832 stands by 529 (days from 19.01.2019 to 01.07.2020) + 303 (days from 19.06.2021 to 18.04.2022).
I tried some queries with joins, datediff's, case when conditions but nothing worked. I'll be grateful for any help.

Answer 1

If you don't have a Tally/Numbers table (highly recommended), you can use an ad-hoc tally/numbers table
Example or dbFiddle
Select User_ID
,Days = count(DISTINCT dateadd(DAY,N,Start_Date))
from YourTable A
Join ( Select Top 10000 N=Row_Number() Over (Order By (Select NULL))
From master..spt_values n1, master..spt_values n2
) B
On N<=DateDiff(DAY,Start_Date,End_Date)
Group By User_ID
Results
User_ID Days
1 1477
2 832