The Tale of Tableau, MySQL, and the Perils of Composite Keys

How tutoring can teach even a seasoned veteran of data analysis, there are traps awaiting us when we use different software.

Ah, the joys of tutoring. There’s nothing quite like guiding eager minds through the labyrinth of data analysis and visualization. But every so often, a session takes an unexpected twist, turning into a lesson not just for the student, but for the tutor as well. Recently, I found myself in the midst of such a twist while tutoring a bright student in Tableau. The culprit? Composite keys in her MySQL database. What began as a routine session soon escalated into a dramatic data disaster, providing a stark reminder of the double-edged sword that is the composite key.

The Setup:

My student, let’s call her Nandi was no novice. She had a solid grasp of MySQL and was well on her way to mastering Tableau. She had built a well-structured database with multiple tables, each brimming with meticulously organized data. But as we dove into the world of Tableau, ready to connect those tables and create some visually stunning dashboards, something went terribly wrong.

“Why isn’t the data linking properly?” she asked, her brow furrowed as she stared at the tangled mess of mismatched rows and columns on the screen. I was puzzled too. Everything looked right at first glance. The tables were structured correctly, and the relationships seemed logical. But as we dug deeper, the problem revealed itself: composite keys.