In a small bowl, whisk together the soy sauce, water, sesame oil, sugar, and salt. Set aside until needed.
Heat the 2 tablespoons of oil in a wok or large skillet over medium-high heat. Add the eggs and scramble, breaking them up into small pieces. Transfer the eggs to a bowl and set aside.
Reduce the heat to medium and add the remaining 1 tablespoon of oil. Add the sausage and stir fry for 30 seconds to release some of the fat.
Add the onions and cook until soft and translucent, 3 to 5 minutes.
Increase the heat to high and add the rice. Cook the rice until heated through, stirring often and breaking up any clumps, about 5 minutes.
Pour the reserved sauce over the rice and mix together with a scooping motion. Cook for an additional 1 to 2 minutes.
Add the scrambled eggs and corn and toss to combine and heat through. Serve immediately.