I built my own online CRM to manage clients and events. Sales-men/women were able to uniquely login, view all events, event details (booking status, dates and times, client information, location, etc.), edit event details, sort the events, track financials, view events in a calendar and list form, and more. I couldn’t singlehandedly keep up with the needed updates and changes so discontinued the project. Since 2016, the code had become depreciated and, frankly, a security risk to my server so it can no longer be hosted. However, its legacy continues to impress.
Below is a simple backend for a CRM using Oracle SQL Developer and Java just to demonstrate this skill. Note, the database connection has been redacted.