When you want to enter a set-type constant in an expression, you must give a set constructor. In essence this is the same thing as when you define a set type, only you have no identifier to identify the set with.
A set constructor is a comma separated list of expressions, enclosed in square brackets.
Set constructors
All set groups and set elements must be of the same ordinal type.
The empty set is denoted by [], and it can be assigned to any type of set. A set group with a range [A..Z] makes all values in the range a set element. If the first range specifier has a bigger ordinal value than the second the set is empty, e.g., [Z..A] denotes an empty set.
The following are valid set constructors:
