Every column in a table must have a data type. The choice of data type is important for the following reasons:
For example, you cannot apply aggregate functions, such as SUM, to columns that are defined on a character data type.
The space required to accommodate data items is not as important for small tables as it is for tables with hundreds of thousands of rows. When a table reaches that many rows, the difference between a 4-byte and an 8-byte data type can be crucial.
Figure 22 shows a decision tree that summarizes the choices among built-in data types. The choices are explained in the following sections.