SQL Project Planning

VIEW and CTEs

Question Link

You are given a table, Projects, containing three columns: Task_ID, Start_Date and End_Date. It is guaranteed that the difference between the End_Date and the Start_Date is equal to 1 day for each row in the table.

If the End_Date of the tasks are consecutive, then they are part of the same project. Samantha is interested in finding the total number of different projects completed.

Write a query to output the start and end dates of projects listed by the number of days it took to complete the project in ascending order. If there is more than one project that have the same number of completion days, then order by the start date of the project.

Sample Input

Sample Output

2015-10-28 2015-10-29
2015-10-30 2015-10-31
2015-10-13 2015-10-15
2015-10-01 2015-10-04

Explanation

The example describes following four projects:

• Project 1: Tasks 1, 2 and 3 are completed on consecutive days, so these are part of the project. Thus start date of project is 2015-10-01 and end date is 2015-10-04, so it took 3 days to complete the project.

• Project 2: Tasks 4 and 5 are completed on consecutive days, so these are part of the project. Thus, the start date of project is 2015-10-13 and end date is 2015-10-15, so it took 2 days to complete the project.

• Project 3: Only task 6 is part of the project. Thus, the start date of project is 2015-10-28 and end date is 2015-10-29, so it took 1 day to complete the project.

• Project 4: Only task 7 is part of the project. Thus, the start date of project is 2015-10-30 and end date is 2015-10-31, so it took 1 day to complete the project.

/*
Write a query to output the start and end dates of projects listed by the number of days
it took to complete the project in ascending order. If there is more than one project
that have the same number of completion days, then order by the start date of the project.
*/

WITH proj_starts AS (
SELECT  
    start_date,
    RANK() OVER (ORDER BY start_date) AS proj_rank_start  -- arbitrary id to be used in joining tables
FROM projects
WHERE start_date NOT IN (SELECT end_date FROM projects)), -- filter projects' start dates
proj_ends AS(
SELECT  
    end_date,
    RANK() OVER (ORDER BY end_date) AS proj_rank_end  -- arbitrary id to be used in joining tables
FROM projects
WHERE end_date NOT IN (SELECT start_date FROM projects))  -- filter projects' end dates
SELECT 
    start_date, 
    end_date 
FROM proj_starts, proj_ends
WHERE proj_rank_start = proj_rank_end
ORDER BY end_date-start_date, start_date;

-- OR
SELECT 
    p2.start_date, 
    (
    SELECT 
        MIN(p1.end_date)
    FROM projects p1 
    WHERE p1.end_date NOT IN (SELECT start_date FROM projects) 
    AND p1.end_date > p2.start_date) as q
FROM projects p2
WHERE p2.start_date NOT IN (SELECT end_date FROM projects)
ORDER BY q-p2.start_date, p2.start_date;