Question

What’s the term describing the relationship between tables that share a common primary key?

Here’s an example:

Table 1
property(property_id, property_location, property_price, …);

Table 2
flat(property_id, flat_floor, flat_bedroom_count, …);

Answer 1

What you have looks like table inheritance. If your table structure is that all flat records represent a single property but not all property records refer to a flat, then that’s table inheritance. It’s a way of modeling something close to object-oriented relationships (in other words, flat inherits from property) in a relational database.