This repository hosts some of my solutions to the problems on the SQLzoo.net site. I won't put quiz answers here as well as the trivial queries that either are already given or require minimal changes.
I realized that there are not many SQL questions labeled "interview". Otherwise, there are plenty of problems which I will try to solve efficiently and post my solutions here. Once I run out of freemium problems, I will use my .edu account for the premium discount.
Update: The editor now uses PostgreSQL. One of the problems has been removed from the site so the there is no number associated with it.
Most of the easy problems are trivial as certain groups of consecutive problems would only have one basic change between them. I will not post those. Instead, I will post the alternative queries, the medium problems and any problem I liked. Even if some problems were labeled easy, difficulty is relative. I earned the 5 star gold badge for SQL in less than a week while working on StrataScratch problems. Although there are user submissions on StrataScratch, many are not upvoted as the most optimal when compared to Hackerrank. However, they are not the same problems so perhaps StrataScratch can benefit from more publicity. Also, free access on both sites contain about the same number of problems but most of the Hackerrank problems are meant to check fundamentals. Later on, the Hackrrank problems are just poorly worded.
A warning: The built in Codewars IDE does not support MySQL and primarily supports PostgreSQL instead. I do not mind this change as I see a growing popularity with PostgreSQL in tech stacks compared to MySQL. More importantly, this platform forces me to use pure SQL to solve problems without built in functions. I believe that if I do not implement or at least understand the base solution then I have not earned the privilege to use the respective built in function.
I had made a separate repository for all Codewars problems that I completed but that has been discoruaged by Codewars. My profile name is Porkdown and I worked on Python and SQL problems. Since this is a SQL repository for my daily challenges I will upload some of my solutions here but I will not change the name of the repository so that people cannot find the solutions. The problems on this site have weird difficulty rating from 6-8 kyu but the wording is much better than Hackerrank. My suggestion for using this platform is to go up two kyus above your current kyu and try the most popular problem or kata. If that is too hard go down one kyu until it is solvable. Kyu progresses in a descending order from 8 kyu which is trivial to 1 kyu which is the hardest. Starting with higher kyu is better since you rank up faster. If two kyu above is too easy then I reccomend looking for another site since there are not many extreme problems.