HackerRank: SQL - All solutions (Basic Select, Advanced Select, Aggregation, Basic Join, Advanced Join, Alternative Queries)

I have tried to provide the complete solution with possible explanation to all SQL Practice problem on HackerRank. 

While solving all SQL problems from HackerRank, I came across multiple solutions for the same problem. I tried to provide those with explanation. 

Please checkout my solutions and make use of it for the learning purpose only. In case of any double, feel free to drop a comment on a respective blog post. I will try my best to resolve your query.

Recommended SQL Courses:

1. Udemy: SQL - MySQL for Data Analytics and Business Intelligence
2. LinkedIn: Master SQL for Data Science
3. edX: Databases: Advanced Topics in SQL
4. edureka: SQL Essentials Training & Certification
5. Coursera: Learn SQL Basics for Data Science
6. Eduonix: SQL Queries

=== INTERVIEW QUESTIONS ===

1. Bank Accounts Summary

=== BASIC SELECT ===

1. Revising the Select Query I
   
2. Revising the Select Query II
   
3. Select All
   
4. Select By ID
   
5. Japanese Cities' Attributes
   
6. Japanese Cities' Names
   
7. Weather Observation Station 1
   
8. Weather Observation Station 3
   
9. Weather Observation Station 4
   
10. Weather Observation Station 5
    
11. Weather Observation Station 6
    
12. Weather Observation Station 7
    
13. Weather Observation Station 8
    
14. Weather Observation Station 9
    
15. Weather Observation Station 10
    
16. Weather Observation Station 11
    
17. Weather Observation Station 12
    
18. Higher Than 75 Marks
    
19. Employee Names
    
20. Employee Salaries

=== ADVANCED SELECT ===

1. Type of Triangle
   
2. The PADS
   
3. Occupations
   
4. Binary Tree Nodes
   
5. New Companies

=== AGGREGATION ===

1. Revising Aggregations - The Count Function
   
2. Revising Aggregations - The Sum Function
   
3. Revising Aggregations - Averages
   
4. Average Population
   
5. Japan Population
   
6. Population Density Difference
   
7. The Blunder
   
8. Top Earners
   
9. Weather Observation Station 2
   
10. Weather Observation Station 13
    
11. Weather Observation Station 14
    
12. Weather Observation Station 15
    
13. Weather Observation Station 16
    
14. Weather Observation Station 17
    
15. Weather Observation Station 18
    
16. Weather Observation Station 19
    
17. Weather Observation Station 20

=== BASIC JOIN ===

1. Asian Population
   
2. African Cities
   
3. Average Population of Each Continent
   
4. The Report
   
5. Top Competitors
   
6. Ollivander's Inventory
   
7. Challenges
   
8. Contest Leaderboard

=== ADVANCED JOIN ===

1. SQL Project Planning
   
2. Placements
   
3. Symmetric Pairs
   
4. Interviews
   
5. 15 Days of Learning SQL

=== ALTERNATIVE QUERIES ===

1. Draw The Triangle 1
   
2. Draw The Triangle 2
   
3. Print Prime Numbers

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