UNSIGNED only stores positive numbers (or zero). On the other hand, signed can store negative numbers (i.e., may have a negative sign ).
Here's a table of the ranges of values each
INTEGER type can store:
UNSIGNED ranges from
n , while signed ranges from about
In this case, you have an
AUTO_INCREMENT ID column, so you would not have negatives. Thus, use
UNSIGNED. If you do not use
UNSIGNED for the
AUTO_INCREMENT column, your maximum possible value will be half as high (and the negative half of the value range would go unused).