If you’ve ever joined two tables based on a foreign key and still got wrong results — this post is for you.
The Assumption Most of Us Start With
· Relationships live in schemas
· Foreign keys tell the truth
· ER diagrams reflect reality
Where It Breaks in Real Systems
· Columns reused over time
· Foreign keys dropped “temporarily” for performance
· Documentation not updated
· Systems integrated without shared ownership
Schemas age faster than data.
The Shift: From “Defined” to “Observed”
· Don’t ask “Is there a relationship?”
· Ask “Do these fields behave like they’re related?”
Practical Takeaway
In the next post, I’ll break down the field-level signals we actually use to infer relationships — without relying on names or metadata.
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