Hi Suprita, can you share an example with numbers, preferably in a .twbx workbook? It is difficult to give a general answer without knowing the specifics of all the dimensions and parameters involved.
That aggregate exists for the sheet it was based on (and perhaps on other sheets that have the same filters applied to them). Within the context of that sheet you will be able to use that aggregate in other calcs -- including calcs that pull in the value of the user's input for a parameter.
But you can't store that value and then reuse it somewhere outside the context of that sheet.
Is it possible that we store the aggregate value in a table (may be using a sql query if it works in tableau?) and then merge it with our existing data source to create a new column in the data source itself?
Tableau doesn't write data. Tableau only reads data. It's a one-way tool.