Relations are what turn a set of tables into a real system, not just several lists.
Relation types
- One-to-one — one record is linked to exactly one record in another table.
- One-to-many — one record (for example, a Client) is linked to several records in another table (for example, several Projects of that client).
- Many-to-many — records on both sides can be linked freely (for example, a Project can use several Materials, and a Material can be used in several Projects).
Inverse field
If a Project has a relation field “Client”, the Clients table automatically gets an inverse field — a list of all Projects for that client. Through that inverse field you can add new related records right from the parent record card — for example, add a new expense line from the project page without opening the Expenses table.
Formulas across relations
Once the relation is in place, you can build formulas that calculate over related records — for example, SUM(expenses.amount) totals all expenses linked to the project, and budget - SUM(expenses.amount) shows the remaining budget. See How formulas work.