I don't know enough about web development yet to get my logic straight, but I'm sure you do. I'll try to make this brief.

Two TextBoxes populate my Parameters for an Oracle query - neither TextBox is required - if they are both empty my query will return everything and will take some time to execute. My search button runs the query and is a trigger for an UpdatePanel that holds the populated GridView.

Everything works fine, except I want to do this:

If both TextBoxes are empty, I'd like to warn the user that this could take some time - do you want to execute the query or forget it and fill in some values in the TextBox(es)?

I realize the two technologies that I'll need to use are both client side and server side, so I need some help.
-Do I popup a confirm from the codebehind and go from there? Can I even get the users click value?
-Check the TextBoxes from the clientside and call my codebehind if the user clicks ok? Can I do this?
-Do something completely different?

Let me know if I didn't explain that well. Thanks for pushing this chump web developer in the right direction!