SQL Practical Query Problems

Avoid double-counting payments and refunds

Pre-aggregates two one-to-many relationships before joining them to prevent fanout from corrupting financial totals.

Build daily order KPIs with conditional aggregation

Builds several daily business metrics in one grouped query while keeping each metric definition explicit.

Calculate a running account balance

Uses an ordered window aggregate to calculate a deterministic running balance per account.

Calculate seven-day rolling revenue

Combines daily aggregation, a calendar table, and a window frame to calculate true seven-calendar-day revenue.

Detect overlapping bookings for a resource

Implements correct half-open interval overlap logic for booking validation.

Filter orders by line item without duplicate orders

Uses EXISTS instead of a row-multiplying join when the related table is only a filter.

.NET Full Stack

Full-cycle .NET full-stack interview preparation.

A role-based preparation path covering C#, ASP.NET Core APIs, data access, frontend integration, testing, deployment, system design, real-life scenarios, and behavioral interview topics.

.NET Backend