declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
	execute immediate 'ALTER TABLE PTOVTA_SEGURO ADD ( INDESTANSEGTABELA NUMBER(1, 0) DEFAULT 0 )';
    exception when column_exists then null;
end;
/
declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
	execute immediate 'ALTER TABLE PTOVTA_SEGURO ADD ( INDESTANSEGTABELA NUMBER(1, 0) DEFAULT 0 )';
    exception when column_exists then null;
end;