declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE TARIFA_OFICIAL ADD (COMPOSICAO_DO_PEAJE VARCHAR(100))';
    exception when column_exists then null;
end;
/
declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE TARIFA ADD (COMPOSICAO_DO_PEAJE VARCHAR(100))';
    exception when column_exists then null;
end;