In which cases is it recommended to use traversal tables (side tables) in a database?

Side tables (or auxiliary tables) in a database are used to store additional information that does not fit or is not practical to store in the main table. They are recommended in the following cases:

• Schema extension without changing the main table. For example, when you need to add many optional or rarely used fields.
• Storing data with different structures. If different records have different sets of attributes, a side table allows storing them in a key-value format.
• Isolation of large or rarely used data. To avoid cluttering the main table and improve performance.
• Implementation of many-to-many relationships. Such relationships are often implemented through separate link tables.

Example: In an iOS application, you have a main users table, and a side table stores settings or additional parameters that are not needed for all users.

This helps maintain the flexibility and scalability of the database, as well as optimize queries and storage.