Preheat oven to 400 degrees.
Roughly crush pretzels, and combine with 1/2 cup sugar and melted butter. Press into the bottom of a 9×13 baking dish. Bake for 7 minutes, cool. Break into pieces, and set aside in an air tight container until ready to use.
Beat Cream Cheese and 1/2 cup sugar until creamy. Fold in pineapple and cool whip. Chill.
Before serving, stir 3/4 pretzel mixture in, top with remaining to serve.