The smallest unit of data that can be manipulated in SQL is called a value. Values are interpreted according to the data type of their source.
- Special registers
- Variables (such as host variables, SQL variables, global variables, parameter markers, module variable, and parameters of routines)
- Boolean values
All data types include the null value as a possible value. The null value is a special value that is distinct from all non-null values and thereby denotes the absence of a (non-null) value. Although all data types include the null value, a column defined as NOT NULL cannot contain null values.
A Unicode database also supports national character strings that are synonyms for graphic strings.
Built-in and user-defined data types