How to join transactional data with customer data tables and perform case-based operations in SQL - sql

Question

I'm trying to perform a query between two different tables and come up with a case by case scenario, coming up with a list of records of calls for a specific month.
Here are my tables:
Customer table:
+----+----------------+------------+
| id | name | number |
+----+----------------+------------+
| 1 | John Doe | 8973221232 |
| 2 | American Dad | 7165531212 |
| 3 | Michael Clean | 8884731234 |
| 4 | Samuel Gatsby | 9197543321 |
| 5 | Mike Chat | 8794029819 |
+----+----------------+------------+
Transaction data:
+----------+------------+------------+----------+---------------------+
| trans_id | incoming | outgoing | duration | date_time |
+----------+------------+------------+----------+---------------------+
| 1 | 8973221232 | 9197543321 | 64 | 2018-03-09 01:08:09 |
| 2 | 3729920490 | 7651113929 | 276 | 2018-07-20 05:53:10 |
| 3 | 8884731234 | 8973221232 | 382 | 2018-05-02 13:12:13 |
| 4 | 8973221232 | 9234759208 | 127 | 2018-07-07 15:32:30 |
| 5 | 7165531212 | 9197543321 | 852 | 2018-08-02 07:40:23 |
| 6 | 8884731234 | 9833823023 | 774 | 2018-07-03 14:27:52 |
| 7 | 8273820928 | 2374987349 | 120 | 2018-07-06 05:27:44 |
| 8 | 8973221232 | 9197543321 | 79 | 2018-07-30 12:51:55 |
| 9 | 7165531212 | 7651113929 | 392 | 2018-05-22 02:27:38 |
| 10 | 5423541524 | 7165531212 | 100 | 2018-07-21 22:12:20 |
| 11 | 9197543321 | 2983479820 | 377 | 2018-07-20 17:46:36 |
| 12 | 8973221232 | 7651113929 | 234 | 2018-07-09 03:32:53 |
| 13 | 7165531212 | 2309483932 | 88 | 2018-07-16 16:22:21 |
| 14 | 8973221232 | 8884731234 | 90 | 2018-09-03 13:10:00 |
| 15 | 3820838290 | 2093482348 | 238 | 2018-04-12 21:59:01 |
+----------+------------+------------+----------+---------------------+
What am I trying to accomplish?
I'm trying to compile a list of "costs" for each of the customers that made calls on July 2018. The costs are based on:
1) If the customer received a call (incoming), the cost of the call is equal to the duration;
2) if the customer made a call (outgoing), the cost of the call is 100 if the call is 30 or less in duration. If it exceeds 30 duration, then the cost is 100 plus 5 * duration of the exceeded period.
If the customer didn't make any calls during that month he shouldn't be on the list.
Examples:
1) Customer American Dad has 3 incoming calls and 1 outgoing call, however only trans_id 10 and 13 are for the month of July. He should be paying a total of 538:
for trans_id 10 = 450 (100 for the first 30s + 5 * 70 for the remaining)
for trans_id 13 = 88
2) Customer Samuel Gatsby has 1 incoming call and 3 outgoing calls, however only trans_id 8 and 11 are for the month of July. He should be paying a total of 722:
for trans_id 8 = 345 (100 for the first 30s + 5 * 49 for the remaining)
for trans_id 11 = 377
Considering only these two examples, the output would be:
+----+----------------+------------+------------+
| id | name | number | billable |
+----+----------------+------------+------------+
| 2 | American Dad | 7165531212 | 538 |
| 4 | Samuel Gatsby | 9197543321 | 722 |
+----+----------------+------------+------------+
Note: Mike Chat shouldn't be on the list as he didn't make or receive any calls for that specific month.
What have I tried so far?
I've been playing cat and mouse with this one, I'm using the number as uniqueID, already attempted both a full outer join and combining where incoming or outgoing is not null then applying rules by case, tried doing a left join and applying cases, but I'm circling around and I can't get to a final list. Whenever I get incoming or outgoing, I'm either not able to apply the case or not able to come with both together. Really appreciate the help!
select customer_name.name, customer_name.number, bill = (CASE
WHEN customer_name.number = transaction_data.incoming then 'sum bill'
else 'multiply and add'
end)
from customer_name
left join transaction_data on customer_name.number = transaction_data.incoming or customer_name.name = transaction_data.outgoing
where strftime('%Y-%m', transaction_data.date_time) = '2018-07'
Note: I'm using sqlite to try it out online but the database is on SQL Server 2012, so I know that I can use a date format much easier, that way, but I'd like to keep as close to T-SQL as possible.
Also tried creating a case to determine whether it's incoming call or outgoing, but I'm only getting incoming as a result, even though trans_id 10 is outgoing:
select name, number, duration, case
when customer_name.number = transaction_data.incoming then 'incoming'
when customer_name.number = transaction_data.outgoing then 'outgoing'
END direction
from customer_name
left join transaction_data on customer_name.number = transaction_data.incoming or customer_name.name = transaction_data.outgoing
where strftime('%Y-%m', transaction_data.date_time) = '2018-07'

Answer 1

Try this:
SELECT
c."name", c.number,
SUM(CASE c.number
WHEN t.incoming THEN t.duration
ELSE IIF(t.duration - 30 < 0, 0, t.duration - 30) * 5 + 100
END) AS billable
FROM Customer AS c INNER JOIN [Transaction] AS t
ON c.number IN(t.incoming, t.outgoing)
WHERE t.date_time >= '20180701' AND t.date_time < '20180801'
GROUP BY c."name", c.number
Output:
| name | number | billable |
+---------------+------------+----------+
| John Doe | 8973221232 | 440 |
| American Dad | 7165531212 | 538 |
| Michael Clean | 8884731234 | 774 |
| Samuel Gatsby | 9197543321 | 722 |
Test it online with SQL Fiddle.