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Introduction To SQL
SQL stands for Structured Query Language. SQL is used to create, remove, alter the database and database objects in a database management system and to store, retrieve, update the data in a database. SQL is a standard language for creating, accessing, manipulating database management system. SQL works for all modern relational database management systems, like SQL Server, Oracle, MySQL, etc.
- It is a standard language for Relational Database System. It enables a user to create, read, update and delete relational databases and tables.
- All the RDBMS like MySQL, Informix, Oracle, MS Access and SQL Server use SQL as their standard database language.
- SQL allows users to query the database in a number of ways, using English-like statements.
Link for the Problem – SQL Project Planning – Hacker Rank Solution
SQL Project Planning – Hacker Rank Solution
Problem:
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.
SQL Project Planning – Hacker Rank Solution
SELECT START_DATE, MIN(END_DATE)
FROM
(SELECT START_DATE
FROM PROJECTS
WHERE START_DATE NOT IN
(SELECT END_DATE
FROM PROJECTS)) A,
(SELECT END_DATE
FROM PROJECTS
WHERE END_DATE NOT IN
(SELECT START_DATE
FROM PROJECTS)) B
WHERE START_DATE < END_DATE
GROUP BY START_DATE
ORDER BY (MIN(END_DATE) - START_DATE), START_DATE;
