Table salt, sea salt, and kosher salt are all the same thing: sodium chloride. And they all have the same sodium content (40%). The differences are primarily in texture and taste.
Table salt is made from rock salt harvested from inland deposits (with iodine sometimes added as an extra nutrient). Kosher salt is made from similar sources, but it's usually additive-free and has a coarser texture. Sea salt, as its name suggests, is harvested from evaporated seawater. Consequently, it has a slightly different flavor. In the end, though, they all contribute equally to your total sodium consumption.