Example 1: Undeclaring variables in interactive SQL

    SQL> ATTACH 'FILENAME personnel';
    SQL>
    SQL> DECLARE :X INTEGER;
    SQL> DECLARE :Y CHAR(10);
    SQL>
    SQL> BEGIN
    cont>   SET :X = 100;
    cont>   SET :Y = 'Active';
    cont> END;
    SQL> PRINT :X, :Y;
               X   Y
             100   Active
    SQL> SHOW VARIABLES
    X                               INTEGER
    Y                               CHAR(10)
    SQL> UNDECLARE :X, :Y;