Comment by Stitch4223

One example is that in ER cardinality is specified on the relation. In SQL cardinality is implemented and can be largely reversed to ER by looking at where foreign keys are.

Many to many will lead to an extra table (which can have additional properties, requiring this table to be modelled as an entity), one to many leads to the inclusion of a foreign key to another unique key (referring all columns of that key, _id is an implementation decision, compound primary keys are possible). One to one can be implemented in multiple ways, like one to many with a uniqueness constraint by the referring table or even by merging entities to a single table.

The raw SQL can be revealing but when entities have merged into one table it’s harder to tell what is what, unless a certain set of columns appears over different tables.