Comment by SigmundA

I don't agree, a relational database is not required to have a particular storage engine or format, that is an implementation detail.

There are other relational databases that have both kinds of storage engines and some use both on the same table (row based insert with column based migration and secondary column store indexes: https://learn.microsoft.com/en-us/sql/relational-databases/i...

Just like you can have b-tree based table storage vs heap in the case of index organized tables / clustered indexes (which pg doesn't have) you can choose column based instead the logical data model is still the same relational model.