It looks dataview is using double for DECIMAL now. It causes a problem that
it can not store exact value over 16 digit.

org/netbeans/modules/db/dataview/util/DBReadWriteHelper.java:

                case Types.DECIMAL:
                    numberObj = (valueObj instanceof Number) ? (Number) valueObj : new BigDecimal(valueObj.toString());
                    ps.setDouble(index, numberObj.doubleValue());
                    break;

The above codes should be following. Another point is, it's better to
use Long for BIGINT.

                case Types.BIGINT:
                    numberObj = (valueObj instanceof Number) ? (Number) valueObj : new Long(valueObj.toString());
                    ps.setLong(index, numberObj.doubleValue());
                    break;

                case Types.DECIMAL:
                case Types.NUMERIC:
                    BigDecimal bigDec = new BigDecimal(valueObj.toString());
                    ps.setBigDecimal(index, bigDec);
                    break;

This issue has been reported from community user in Japan.