What is the difference between these corns?

The basic difference between sweet corn and other corns is that sweet corn is harvested while the grain is still soft and the sugars have not yet converted to starch. There are, of course, many different varieties of corn. Some are more suitable for harvesting as sweet corn and others are best left till fully ripe to be ground into flour or meal.

for me there are two types of corn the native one and the imported one that usually came from the other country such as the Japanese corn,the native one is small compare to the Japanese corn and the Japanese corn is more sweet compare to native corn.

I don't really know the difference between corns but I think all corns are created the same except that they differ in texture and sweetness. As for me I always prefer the native white corn (such s that in the attached photo), more than the yellow or Japanese corn. I am not so happy with Japanese corn because even if they are sweet they can't seem to fill unlike the white corn which are very sweet when newly harvest and at the same time they are filling.

Sweet corn is processed differently which is why it has a different taste. I perfer the sweet corn myself.