Rollups — Sterodata docs

A rollup works out a figure over the records that link to this one: how many orders a customer has, what a tenancy has paid, the date of the latest visit.

A link goes one way: each order points at its customer. A Rollup answers from the other end. Added to Customers, it reads the orders that link to each customer and gives one figure per customer: their number of orders, the sum of their amounts, the date of the last one. It is worked out each time the table is read, so it is always current, and nobody types in it.

Add a rollup

In the table the links point at, such as Customers, choose + at the right of the headers. Name the field, such as Total ordered, and pick the type Rollup.
Under Rows of, pick the table whose records link here, such as Orders. A table or a Dynamic table can be picked; a summary cannot.
Under Linked by, pick its link that points at this table, such as Customer. If it has none, Sterodata says so: add the link to that table first.
Under Calculate, pick what to work out, and under Of, the field to work it out from. The table below lists the choices.
If you want, use Limit records to count only some of the rows, such as orders whose Status is Paid.
Choose Save.

Calculate	What it gives	Of
Sum	The values added up. A customer with no orders gets 0.	A number, percent or currency field
Count of rows	How many rows link here.	No field needed
Smallest	The lowest value.	A number, percent, currency or date field
Largest	The highest value.	A number, percent, currency or date field
Average	The average of the values.	A number, percent or currency field
Latest	The value of the row that comes last by the field under By, such as the status of the most recent visit.	Any field holding one value: text, a choice, a link, a date, an amount
Earliest	The value of the row that comes first by the field under By.	The same as Latest

For Latest and Earliest, By is the date or number that puts the rows in order. When the table has one date field, it is picked for you. Rows with nothing in that field are left out.

A calculation or another rollup of the other table can be rolled up too, by what it gives.

Amounts in several currencies

When Of is a currency field, Answer in sets the currency the rollup answers in, the field's own to start with. Amounts in other currencies are converted into it. See Calculations for how amounts convert and what a total shows while a rate is missing.

Using a rollup

A rollup can be sorted, filtered and read in a formula like a stored number, and its column's total adds up when it answers in amounts. It cannot be grouped by.

A person who may read the table can read its rollups without being able to open the table they come from. A rollup over a field hidden from them is hidden from them too.

A rollup that would read itself, through a chain of other rollups, is refused, and the refusal names the chain.