solve: questions faizanxmulla#11, faizanxmulla#12

Author: faizanxmulla

ankit-bansal-sql/medium-complex-sql-questions-playlist/11-l&t-highest-lowest-salary.md

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+### Problem Statement
+
+Write a query to print the highest and lowest salary of each employee in each department.
+
+
+### Schema Setup
+
+```sql
+CREATE TABLE employee (
+    emp_name VARCHAR(10),
+    dep_id INT,
+    salary INT
+);
+
+DELETE FROM employee;
+
+INSERT INTO employee VALUES 
+('Siva', 1, 30000),
+('Ravi', 2, 40000),
+('Prasad', 1, 50000),
+('Sai', 2, 20000);
+```
+
+
+### Expected Output
+
+dep_id | emp_name_max_salary | emp_name_min_salary |
+--|--|--|
+1 | Prasad |  Siva |
+2 | Ravi | Sai |
+
+
+### Solution Query
+
+```sql
+-- Solution 1: using two RANK() functions; and aggregation function w/ CASE WHEN // aslo my approach
+
+WITH CTE as (
+    SELECT *, 
+           RANK() OVER(PARTITION BY dep_id ORDER BY salary desc) as highest_rn, 
+           RANK() OVER(PARTITION BY dep_id ORDER BY salary) as lowest_rn
+    FROM   employee
+)
+SELECT   dep_id,
+         MAX(CASE WHEN highest_rn=1 THEN emp_name END) AS emp_name_max_salary,
+         MAX(CASE WHEN lowest_rn=1 THEN emp_name END) AS emp_name_min_salary
+FROM     CTE
+GROUP BY 1
+
+
+-- Solution 2: almost the same approach
+
+WITH CTE as (
+    SELECT   dep_id, MAX(salary) as max_salary, MIN(salary) as min_salary
+    FROM     employee
+    GROUP BY 1
+)
+SELECT   dep_id,
+         MAX(CASE WHEN salary=max_salary THEN emp_name ELSE NULL END) AS emp_name_max_salary,
+         MAX(CASE WHEN salary=min_salary THEN emp_name ELSE NULL END) AS emp_name_min_salary
+FROM     employee e JOIN CTE c USING(dep_id)
+GROUP BY 1
+ORDER BY 1
+```

ankit-bansal-sql/medium-complex-sql-questions-playlist/12-call-start-end-time.md

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+### Problem Statement
+
+Write a query to get `start time` and the `end time` of each call from the below 2 tables. 
+
+Also create a column of call duration in minutes. 
+
+**NOTE:** Please do take into account there will be multiple calls from phone number and each entry in `start` table has a corresponding entry in the `end` table.
+
+
+### Schema Setup
+
+```sql
+CREATE TABLE call_start_logs(
+    phone_number VARCHAR(10),
+    start_time TIMESTAMP
+);
+
+CREATE TABLE call_end_logs(
+    phone_number VARCHAR(10),
+    end_time TIMESTAMP
+);
+
+
+INSERT INTO call_start_logs VALUES
+('PN1', '2022-01-01 10:20:00'),
+('PN1', '2022-01-01 16:25:00'),
+('PN2', '2022-01-01 12:30:00'),
+('PN3', '2022-01-02 10:00:00'),
+('PN3', '2022-01-02 12:30:00'),
+('PN3', '2022-01-03 09:20:00');
+
+INSERT INTO call_end_logs VALUES
+('PN1', '2022-01-01 10:45:00'),
+('PN1', '2022-01-01 17:05:00'),
+('PN2', '2022-01-01 12:55:00'),
+('PN3', '2022-01-02 10:20:00'),
+('PN3', '2022-01-02 12:50:00'),
+('PN3', '2022-01-03 09:40:00');
+```
+
+
+### Expected Output
+
+phone_number |	start_time |	end_time |	call_minutes |
+--|--|--|--|
+PN1 |	2022-01-01T10:20:00.000 |	2022-01-01T10:45:00.000 |	25.00 |
+PN1 |	2022-01-01T16:25:00.000 |	2022-01-01T17:05:00.000 |	40.00 |
+PN2 |	2022-01-01T12:30:00.000 |	2022-01-01T12:55:00.000 |	25.00 |
+PN3 |	2022-01-02T10:00:00.000 |	2022-01-02T10:20:00.000 |	20.00 |
+PN3 |	2022-01-02T12:30:00.000 |	2022-01-02T12:50:00.000 |	20.00 |
+PN3 |	2022-01-03T09:20:00.000 |	2022-01-03T09:40:00.000 |	20.00 |
+
+
+### Solution Query
+
+```sql
+-- Solution 1: using ROW_NUMBER() & JOIN // also my approach
+
+WITH start_logs_cte as (
+    SELECT *, 
+           ROW_NUMBER() OVER(PARTITION BY phone_number ORDER BY start_time) as start_rn
+    FROM   call_start_logs
+)
+, end_logs_cte as (
+    SELECT *, ROW_NUMBER() OVER(PARTITION BY phone_number ORDER BY end_time) as end_rn
+    FROM   call_end_logs
+)
+SELECT   sl.phone_number, 
+         start_time, 
+         end_time, 
+         ROUND(EXTRACT(EPOCH FROM AGE(end_time, start_time)) / 60, 2) as call_minutes
+FROM     start_logs_cte sl JOIN end_logs_cte el ON sl.start_rn=el.end_rn and sl.phone_number=el.phone_number
+ORDER BY 1, 2
+
+
+-- Solution 2: using UNION ALL
+
+WITH CTE as (
+    SELECT phone_number,
+           start_time as call_time, 
+           ROW_NUMBER() OVER(PARTITION BY phone_number ORDER BY start_time) as rn
+    FROM   call_start_logs
+    UNION ALL
+    SELECT phone_number,
+           end_time as call_time, 
+           ROW_NUMBER() OVER(PARTITION BY phone_number ORDER BY end_time) as rn
+    FROM   call_end_logs
+)
+SELECT   phone_number,
+         MIN(call_time) as start_time,
+         MAX(call_time) as end_time,
+         ROUND(EXTRACT(EPOCH FROM AGE(MAX(call_time), MIN(call_time))) / 60, 2) as call_minutes
+FROM     CTE
+GROUP BY phone_number, rn
+ORDER BY 1, 2
+```