how to save multiple file paths in sql database column when user uploads multiple attachments using file upload control?

Well, you have two options. One : choose a character that is not valid for a file path, like ?, and use that as a delimiter to store a list that needs to be split. Second, create a mapping table so you can map multiple file paths to one entry by it's id. So your main table has an id column and your new table contains that id, and a file path, with one entry per path.