Salting and draining the zucchini beforehand prevents this summer salad from getting watery.
Toss zucchini with 1 teaspoon salt in a colander set over a bowl. Let stand 45 minutes. Rinse, then drain and pat very dry.
Meanwhile, bring a large pot of salted water to a boil. Add beans; return to a boil, then cook until crisp-tender, about 2 minutes. Remove with a slotted spoon and run under cold water to stop cooking. Drain; pat dry. Add corn to water and simmer 1 to 2 minutes. Run under cold water to stop cooking; pat dry. On a small baking sheet, stand 1 ear on its end. With a sharp knife, slice downward on all sides, keeping blade against it to remove as many kernels as possible. Repeat with other ear.
In a large bowl, toss beans and zucchini with oil, herbs, and vinegar; season with salt and pepper. Gently fold in corn. Serve immediately, or refrigerate in an airtight container up to 1 day.