Every value in SQL belongs to some data type. A data type
is associated with each value retrieved from a table, each constant,
and each value computed in an expression.
This chapter discusses data types. The following sections
are presented:
A data type defines a set of values. Reference to a previously
defined data type is a convenient way of specifying the set of values
that can occur in some context. For example, in SQL the type INTEGER is defined as the set of integers from -2,147,483,648
through +2,147,483,647, plus the special value NULL. If you define a column with type INTEGER, each value stored in the column must be either
an integer in the range -2,147,483,648 through +2,147,483,647,
or a null value (if NOT NULL is not specified).
