100 Days of SQL : Ace The SQL Interviews Like a PRO!!

Learn how to use self join in sql by joining the employee table to itself with aliases E and M, and identify employees whose salary exceeds their manager’s salary.

Use a common table expression to identify each customer's first visit date, then count new and repeat customers by order date with case statements and aggregation.

Solve scenario-based sql questions by identifying each person's most visited flow and total visits. List distinct resources used with a step-by-step approach using rank and string_agg.

Learn how to pivot and unpivot data in SQL by turning rows into columns and back without built-in pivot functions, using case with sum and union all.

Solve an Amazon interview question: compute the nth Sunday after a given date using datepart and weekday functions, then dateadd to advance weeks across SQL dialects.

Apply the Pareto principle in SQL to identify the top 20% of products driving 80% of sales, using running totals and window functions on a three-year, 2000-product dataset.

Identify persons whose friends' total scores exceed 100, returning their id, name, number of friends, and the total of their friends' scores using joins, aggregation, and a having clause.

Discover when to use where versus having to filter data in SQL, with row-level filters on salaries and aggregation-based filters on department averages.

Learn to compute daily cancellation rates for unbanned clients and drivers by joining trips with users in a sql context, counting cancellations by status, and deriving percentages.