| # | Title | Solution | Difficulty |
|---|---|---|---|
| 176 | Second Highest Salary | MySQL, Oracle, PostgreSQL | Easy |
| 183 | Customers Who Never Order | MySQL | Easy |
| 185 | Department Top Three Salaries | Oracle, PostgreSQL | Hard |
| 578 | Get Highest Answer Rate Question | MySQL | Median |
| 597 | Friend Requests I: Overall Acceptance Rate | MySQL | Easy |
| 602 | Friend Requests II: Who Has the Most Friends | MySQL | Median |
| 511 | Game Play Analysis I | MySQL | Easy |
| 512 | Game Play Analysis II | MySQL | Easy |
| 534 | Game Play Analysis III | MySQL | Medium |
| 550 | Game Play Analysis IV | PostgreSQL | Medium |
| 569 | Median Employee Salary | MySQL | Hard |
| 570 | Managers with at Least 5 Direct Reports | MySQL | Medium |
| 574 | Winning Candidate | MySQL | Medium |
| 577 | Employee Bonus | MySQL | Easy |
| 578 | Get Highest Answer Rate Question | MySQL | Medium |
| 580 | Count Student Number in Departments | MySQL | Medium |
| 584 | Find Customer Referee | MySQL | Easy |
| 585 | Investments in 2016 | MySQL | Medium |
| # | Problem | Solution | Concept/Comment |
|---|---|---|---|
| 1 | User Status | MySQL | |
| 2 | Recommend pages your friends liked | MySQL | |
| 3 | Advertiser spend and ROI metrics | MySQL | subquery |
| 4 | Friends' Messages | Postgres | |
| 5 | Content Actions (Comments per Story) | MySQL, PostgreSQL | left join |
| 6 | Click Through Rate | MySQL, Postgres | group by, sum |
| 7 | Friend Acceptance Rate Trending | PostgreSQL | subquery(left join) group by |
| 8 | Carrier | MySQL | case study |
| 9 | Comments on Post | MySQL | similar to #5 |
| # | Problem | Solution | Concept/Comment |
|---|---|---|---|
| 1 | customers not making purchase | MySQL |
| # | Problem | Solution | Concept/Comment |
|---|---|---|---|
| 1 | Video | Postgres | sum, find max |