Parameter and Keyword Description:
This identifies the user-defined type specifier that is used in the subsequent declarations of the records.
This constraint prevents the assigning of the nulls to the field. At the run time, trying to assign the null to a field, defined as NOT NULL raises the predefined exception VALUE_ ERROR. The constraint NOT NULL should be followed by an initialization clause.
The datatype is a type specifier.
:= | DEFAULT:
This keyword or operator allows you to initialize the fields to the default values.
This is a indiscriminately complex combination of the constants, variables, literals, operators, & function calls. The easiest expression consists of a single variable. When the declaration is explained, the value of the expression is assigned to the field. The value and the field should have the compatible datatypes.