private static int ymdToUnixDate(int year, int month, int day) {
    final int julian = ymdToJulian(year, month, day);
    return julian - EPOCH_JULIAN;
  }
Converts the Java type used for UDF parameters of SQL TIMESTAMP type ({@link Timestamp}) to
internal representation (long).

<p>Converse of {@link #toSQLTimestamp(long)}.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/util/DateTimeUtils.java