declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE BOLETO ADD (CRO VARCHAR2(4))';
    exception when column_exists then null;
end;
/

declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE CAJA ADD (CRO VARCHAR2(4))';
    exception when column_exists then null;
end;
/

declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE EVENTO_EXTRA ADD (CRO VARCHAR2(4))';
    exception when column_exists then null;
end;