Summary fields vs. aggregate calculations across relationships

Expert

Choose between Summary fields and calculation aggregate functions for cross-record totals, and understand when each approach is correct.

What you'll learn

The key behavioral difference between Summary fields and Sum() calculations
When a Summary field is the correct choice vs. Sum()
Why mixing them in the same context causes confusion

FileMaker offers two ways to compute a total across related records: a Summary field (defined as a type in Manage Database) and a calculation field using aggregate functions like Sum() or Count(). They behave differently, serve different purposes, and choosing wrong leads to incorrect or slow results.

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Summary fields: found-set aggregates

A Summary field is defined with type "Summary" in Manage Database. It aggregates across the current found set of the table it is defined in. On a layout based on that table, it shows the total for all records in the current found set — not just related records.

FileMaker Script

// Summary field: Total of Amount in LineItems table
// On a "LineItems List" layout:
// → Shows total of ALL visible (found-set) line items

// In a Sub-summary part sorted by InvoiceId:
// → Shows total per invoice group