Hi Supriya,
You can find the html input box like this:
Dim SourceTextBox As TextBox
SourceTextBox = CType(FindControl("search_input"), TextBox)
Now you can use SourceTextBox.Text to get selected value and add this to database.
To insert this selected value you can follow below links:
step-by-step procedure to INSERT record to SQL server
insert-data-into-sql-server-using-vbnet
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