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.
Sources include:
Constants
Columns
Functions
Expressions
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
Data
types that are pre-defined for use within the database management system are called built-in data
types. Figure 1 shows the supported built-in data types.Figure 1. Built-in Data Types
Support for the following user-defined data types is also provided:
