Supply chain database

[Manoj]

I want to write a query.
I have a table for original forecast containing due date and quantity.The
other table is Time periods (which has time period number and the beginning
and ending date for that time period).
I want to write a query to get the summation of Quantities for the given
period.
Forecast.Due Date>=Time periods.Beginning date<=Time Period.Ending date and
Time period number= Time periods.Time Period number
I wrote the query but it is giving error.
Could any one please help me out?