First of all is coca a Spanish dish with huge variety. A coca can just as well be made of thin yeast dough with savory topping (similar to an Italian pizza but not necessarily with cheese) as well as sponge-cake-like (leavened just with the beaten eggs or with baking soda) with sweet topping.
Foccacia also comes in many varieties, but typical foccacia is made of yeast dough, about one inch thick, which is sprinkled with olive oil and herbs before baking. Foccacia can also be made thinner and without yeast, but that makes a much crispier bread. It may be topped with other ingredients, but does not have to and if it is topped, it is mostly only a simple topping like olives, onions or cheese. It is usually not eaten alone, but as a side dish. Here is a typical foccacia, topped with black olives.
Pizza dough is very similar to foccacia, but in Italy, a pizza is always much thinner. The thick American style pizza is not common in Italy. Except for the thickness, the difference between foccacia and pizza is much more in the topping. A pizza is almost always topped with at least tomatoes or tomato sauce and cheese and mostly with other savory ingredients.