Entities as primary keys is very good! Though as systems generally handle the data transformation, Im not sure they equate to tables

IMO most analogies kinda fall short, but kinda makes sense in my head is:

Entity as ID; Components as Columns, but only kinda; Systems as Application code or functions

Tables in this database/ECS analogy are just tables here too, or memory rather. The data is often conceptually (and implementation wise) laid out as tables in ECS, too