Rollup
The Rollup function aggregates and looks up data in a second workbook data element.
To learn how to apply the Lookup and Rollup functions without directly using the formula bar, visit Add Columns via Lookup.
Syntax
Rollup(formula, local key 1, external key 1, [local key 2], [external key 2], ...)
Function arguments:
 formula (required)  The formula to compute (or the target column to reference) for the row in the target element.
 local key 1 (required)  The column to use as a join key in the local data element.

external key 1 (required)  The column to use as a join key in the target data element.
 local key 2 + (optional)  An additional column to use as a join key in the local data element.
 external key 2 + (optional)  An additional to use as a join key in the target data element.
Example
Rollup(Sum([Sales Amounts/Sales Amount]), [Order Number], [Sales Amounts/Order Number])
Data is inserted into the Orders table’s [Calc] column from Sales Amount table’s [Sales Amount] column.
The function’s formula parameter uses the Sum function to aggregate values from the Sales Amount table’s [Sales Amount] column.
These two tables are joined using a single set of join keys: Orders’ [Order Number] column is joined with Sales Amounts’ [Order Name] column.
Related Columns