I would like to add a column type formula in a dataset that will allow me to perform an operation similar to the following mysql code:
SELECT Sum(Value) FROM datasetdata Group by RowNumber
what should I enter in the ‘Formula’ part?
Your statement doesn’t really make sense - the datasetdata table is a normalised representation of your data, where the value can come from any column (this is changing in 1.8 as it happens, where the table will be materialised).
Beyond that (and unfortunately) I can’t think of a way to aggregate a column in that fashion - other than to write your own module which accesses the dataset directly (some variant on the datasetview module).
If you do look at that you might want to consider developing it against 1.8, which has the materialised view I mentioned.