Preheat the oven to 350 F. Mix sugar, flour and pineapple juice in a bowl. Stir until smooth. Add canned pineapple pieces to the bowl and stir.
Pour this mixture into a 9*13 baking dish. Sprinkle grated cheese on top.
Mix crushed crackers with melted butter. Spread the crumble topping over the cheddar and place the baking dish in the oven. Bake for 30 minutes. Let the pineapple casserole cool slightly, then cut into pieces and serve.