Explain the working principle of a local key in databases.

A local key in databases is a field or set of fields within a table that are used to establish a relationship with another table. Usually, the local key is the primary key of the current table that is referenced by a foreign key in another table.

The principle of a local key is that it uniquely identifies a record in its table and serves as a point of connection for establishing relationships between tables. For example, if you have a "Users" table with an "id" field (local key), and an "Orders" table with a "user_id" field (foreign key), then "user_id" references "id" in the "Users" table.

In the context of Flutter and local databases (e.g., SQLite), a local key helps efficiently link data and ensure data integrity during queries and updates.