Preheat oven to 400 degrees. Line a 9x13-inch baking pan with parchment paper.
In a medium bowl, stir together pretzel pieces, butter, and 1/2 cup sugar. Transfer mixture to prepared baking pan. Press down gently on it and spread it out some. It does not need to cover the bottom of the pan.
Bake for 7 minutes. Let cool.
In a large bowl, use a hand-held mixer to beat cream cheese and remaining 1/2 cup sugar until smooth and creamy.
Fold in Pineapple and Cool Whip. Refrigerate for at least 1 hour.
Just before serving, crumble the pretzel mixture and mix into pineapple mixture. I like to reserve some of it to sprinkle on top.