`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:

Source: http://dev.mysql.com/doc/refman/5.6/en/integer-types.html

`UNSIGNED`

ranges from `0`

to * n* , while signed ranges from about

`-n/2`

to `n/2`

.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).