declare

    column_exists exception;

    pragma exception_init (column_exists , -01430);

begin

    execute immediate 'ALTER TABLE FISCAL_J1 MODIFY ( NUMSERIENOTAFISCAL VARCHAR2(8) )';

    exception when column_exists then null;

end;
/
declare

    column_exists exception;

    pragma exception_init (column_exists , -01430);

begin

    execute immediate 'ALTER TABLE FISCAL_J2 MODIFY ( NUMSERIENOTAFISCAL VARCHAR2(8) )';

    exception when column_exists then null;

end;