Rollup Field

A rollup field summarizes values from a set of linked records into a single number or value on the parent record. It reaches across a relationship and applies an aggregation — SUM, COUNT, MAX, AND, or a concatenation — to a field in the linked records. Classic example: a "Project" record links to many "Task" records; a rollup on Project can show `SUM(Task.Hours)` for total logged hours, a `COUNT` of tasks, or whether `AND(Task.Done)` is true for all of them. Why it matters: rollups turn a one-to-many relationship into usable summary metrics right in the database, powering dashboards and status fields without exporting to a spreadsheet or writing an automation. Airtable, SmartSuite, and similar tools offer them; Notion does it via rollup properties on related databases. Practical note: a rollup requires an existing link/relation field to roll up through — you can't roll up unrelated tables. It differs from a lookup, which pulls a linked value through unchanged; a rollup aggregates or transforms it.