Formula fields: computed from the record itself

A formula field computes its value from the record's other fields. The demo shop's Orders table has one called To collect:

{Total} * (1 - {Discount} / 100)

Every order shows the discounted amount, nobody types it, and it is correct the instant either input changes — because the value isn't synced by the app, it's computed by the database itself. The column is a real Postgres generated column, maintained on every write. A stored total that drifts out of date is not a failure mode this field has.

The builder and the text mode

Add a field and choose Formula. The editor has two skins that hand off to each other losslessly:

• The builder — the default. You compose the expression as pills: fields, functions, operators, values. A "Reads as" line shows the text it amounts to, and beneath it the editor works the formula through your table's first record, step by step, so you see a real answer before the field exists.
• Edit as text — a plain expression box for typing and pasting. Reference fields as {Field Name}; a one-word name works bare. Completion opens on any word you type — fields insert in their braces, functions with their parenthesis — and mistakes are marked at the exact spot, with the nearest real names offered as one-click repairs.

Either way the type of the result — number, text or date — is inferred from the expression and shown live. There is no type to pick, so none to get wrong.

What the language covers

Deliberately small, and checked before anything is saved:

• Arithmetic — + - * /, parentheses, and & to join anything into text.
• Comparisons and logic — IF(condition, then, else) with = != > >= < <=, combined with AND, OR, NOT; nesting is fine, and SWITCH(value, case, result, …, default) reads better than a ladder of IFs. BLANK() tests an empty cell.
• Text — UPPER, LOWER, TRIM, LEN, LEFT, RIGHT, MID, SUBSTITUTE, FIND, CONCATENATE.
• Numbers — ABS, ROUND, ROUNDUP, ROUNDDOWN, INT, CEILING, FLOOR, MOD, POWER, SQRT, VALUE, MIN, MAX.
• Dates — YEAR, MONTH, DAY, WEEKDAY, DATEADD, DATETIME_DIFF (units: days, weeks, months, years), plus plain date math: {Check-out} - {Check-in} is a number of days, {Placed} + 3 a date.
• The record — RECORD_ID().

A long formula can be written as named steps, one per line, the result last:

nights = DATETIME_DIFF({Check-out}, {Check-in}, "days")
subtotal = nights * {Rate per night}
subtotal + subtotal * 0.14

A formula can read the record's text, number, date and single-select fields (a select reads as its choice's name). It can't read another formula, a lookup or a rollup — no chains in v1 — and both IF branches must produce the same type.

Editing after creation

The expression is editable after creation: open the field, change it, save. The result type re-infers from the new expression — a number formula edited into an IF that returns text becomes a text formula. The one refusal: if a lookup or rollup on another table depends on this field's current type, the type-changing edit is blocked by name until that dependent is adjusted.

What a formula field can't do is convert into an ordinary field or back — the column is a generated expression, not typed-in data. To keep computed values as plain data, add a plain field and paste the column in.

Honest edges

• Division by zero, SQRT of a negative, and VALUE of text that isn't a number all produce a blank, never an error cell.
• A date-and-time field is read in universal time (UTC) inside a formula — the editor discloses this whenever you reference one. A day it derives can differ from the grid near midnight.
• There is no TODAY() or NOW(). A stored, database-maintained column cannot depend on the current moment — the API refuses it plainly (Unknown function "TODAY" in formula.). Formulas that know today's date are on the wishlist; today, "days until deadline" needs a tool that asks on a schedule, like a webhook consumer.
• A formula that doesn't check out — a typo, a type mismatch — is refused at creation with the exact place named. It never half-exists.

Everywhere else, an ordinary field

A formula field filters, sorts, groups and feeds webhook payloads exactly like a plain field of its result type, and reads over the API under its own name:

"Total": 63,
"Discount": 10,
"To collect": 56.7

Writing to it is refused: "To collect" is a formula — it's computed automatically and can't be written to directly. The cell is read-only on screen for the same reason.

When you actually want a different field

A formula sees one record at a time. The moment the calculation crosses a link — the customer's total across orders, the latest delivery date across lines — you want a rollup, or a lookup for a single borrowed value. Formula, lookup or rollup sorts the three in two minutes.