Managing & Using MySQL, 2nd Edition

Numeric Types

Before you create a table, you should know what kind of data you wish to store in the table. Beyond obvious decisions about whether your data is character-based or numeric, you should know the approximate size of the data to be stored. If it is a numeric field, what is its maximum possible value? What is its minimum possible value? Could that change in the future? If the minimum is always positive or zero, you should consider an unsigned type. You should always choose the smallest numeric type that can support your largest conceivable value. If, for example, you have a field that represents the population of a state, use an unsigned INT field. No state can have a negative population. Furthermore, an unsigned INT field is certainly large enough to represent a state’s population, unless that population grows to be roughly the current population of the entire Earth.