In a formula column, the SUM_ELEMENTS() function is used to sum the numerical values of selected columns, including columns containing multiple comma-separated values, such as fields of type Column from a linked table.
Note: Some tools also use the term Rollup for an equivalent function to calculate the sum of elements linked to a table.
Let's take for example a table containing timesheets (number of hours worked per day and per person for a given project, possibly with the associated hourly cost), linked to the projects table.
You want to calculate the total number of hours worked in the project, or even better the total cost taking into account the hourly rate of each person.
The "Cost from timesheets" field here is a of type Column from a linked table which is linked to the Timesheets table and returning the content of the "Cost h x rate" field.
To obtain the total, it is therefore necessary to add a "Total labor cost" field which will sum the elements of the "Cost from timesheets" field.
You may also want to hide the column "Cost from timesheets" so that it does not appear in the end user interface.