In MySQL, decimal(x,y) means that the number stored must have x digits, and y of the x digits must be after the decimal point.
For example, decimal(3, 3) would allow numbers like .329 or .123, but NOT 100.
So, decimal(2,2) is perfect if all of your numbers are going to be .25 or .50 or any other tidy fraction of 1. These are fractions, however; they are not percentages. I don't know if you meant that you wanted to store fractions or percentages, but they are both the same, exception percentages are fractions multiplied by 100.
If you want to store percentages, you could use decimal(2,0), which would allow you to store numbers like 91 or 57.
