The Prestashop Database schema contains all the tables and relations, so its very useful to get a quick view of the tables when you develop a module.
You can download here:
The database structure of PrestaShop 1.7.8.x
The database structure of PrestaShop can be found in install/data/db_structure.sql (1.7.8.x releases example @GitHub).
It is used one time, during the installation of PrestaShop. It contains the structure of almost all tables. If a table needs to be added or modified, this the file you should open.