If you can't join these tables in your datasource (which is the preferred way to do this) then you can blend the two datasources within tableau.
First step is to create two date fields, in the Sales data you use dateparse with you month and year fields like so:
And in your forecast, assuming that the current month is always M, you can use this formula to create the date field:
Then using edit relationships, join the forecast to the sales on these fields.
I've attached a workbook showing the bar chart with existing and forecast values.
Hope that helps, let me know if this doesn't work with your real data.
Forecast Combo.twbx 53.2 KB
Thanks a lot !
It seems to meet my needs !
You're welcome, glad it works for you.
I got another question link to this.
If I want to calculate YTD growth, including the forecasting period, how can I do?
I've tried to sum first the actual + forecast, then do running sum, but with no success.