You can not insert the data in Tableau Viz but you can embed a HTML page in your viz that can insert the value in your database & from that database your viz can take the value of comment. Or you can do this outside the Tableau & insert the value in the same database from visualization is coming. Hope this may help!
Thanks for your quick repsonse Prashant. I am very new to Tableau so would you mind explaining how to do this properly please?
I have never tried that but that is the hint for you. Actually you have to create a dynamic web page with a box & submit button & on submit the value goes to database. This is the same database on which you have create the viz. Now in Tableau you have to create a sheet in which put the column in which the data comment was inserted. Hope this may help!
Tableau is a data visualization tool, so you can not insert the data into a visualization. The process which I was suggested is not a part of Tableau, this is the part of web design in which you are creating a dynamic web page. Tableau is only helping you to embed that page or box of that page into tableau. You can also achieving the same by creating a webpage in which embed the tableau visualization & there create a box with submit button (which is outside the tableau dashboard) & there you can save the comment into your database & from that database take the comment column.
You can learn that how to embed tableau into a web page from here: - Embedding Tableau in Portals, Websites and Applications Video | Tableau Software
& here is the method to insert a webpage into Tableau : - Adding a Web Page to a Dashboard | Tableau Software
Hope you can understand the limitation of a data visualization tool.
I have been looking into this as well, its quite advanced web stuff (well for me anyway) you need to connect your webpage form with an ASP.
I am going to look further into this and see if i can get anything that's half way decent looking.
Anyway, i found this thread with some links and 'how to`s' once i have the webpage ill look to embedding it in Tableau..