MyCATApache/Mycat-Server · error · IllegalArgumentException

Interval string does not match year-month format of 'y-m':

Error message

Interval string does not match year-month format of 'y-m':

What it means

fromYearMonthString parses a '[-]y-m' interval literal such as '3-6'. This IllegalArgumentException is thrown when the input string does not match the year-month regex (yearMonthPattern), e.g. missing the dash, non-numeric parts, or extra text.

Solutions

  1. Fix the input string to the strict '[-]y-m' format, e.g. '3-6' or '-1-2'
  2. Trim surrounding whitespace and remove quotes before parsing
  3. Validate the string against the format with a regex before calling the API

Example fix

// before
CalendarInterval iv = CalendarInterval.fromYearMonthString("3 years 6 months");
// after
CalendarInterval iv = CalendarInterval.fromYearMonthString("3-6");
Defensive patterns

Strategy: validation

Validate before calling

private static final Pattern Y_M = Pattern.compile("^-?\\d+-\\d{1,2}$");
static void requireYearMonth(String s) {
  if (s == null || !Y_M.matcher(s.trim()).matches())
    throw new IllegalArgumentException("expected 'y-m', got: " + s);
}

Type guard

static boolean isYearMonthString(String s) {
  return s != null && s.trim().matches("-?\\d+-\\d{1,2}");
}

Try / catch

try {
  iv = CalendarInterval.fromYearMonthString(s);
} catch (IllegalArgumentException e) {
  log.error("Bad year-month interval '{}': {}", s, e.getMessage());
  iv = CalendarInterval.ZERO;
}

Prevention

When it happens

Trigger: Calling CalendarInterval.fromYearMonthString with a string that fails yearMonthPattern.matcher(s).matches(), e.g. fromYearMonthString("3 years 2 months"), fromYearMonthString("3:6"), fromYearMonthString("3-").

Common situations: SQL interval literals typed in the wrong format in a Mycat SQL query, config values copied from another database dialect, user-supplied input passed straight to the parser.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/a98ec1401142eadb. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/memory/unsafe/types/CalendarInterval.java:116

      }
    }
    return result;
  }

  /**
   * Parse YearMonth string in form: [-]YYYY-MM
   *
   * adapted from HiveIntervalYearMonth.valueOf
   */
  public static CalendarInterval fromYearMonthString(String s) throws IllegalArgumentException {
    CalendarInterval result = null;
    if (s == null) {
      throw new IllegalArgumentException("Interval year-month string was null");
    }
    s = s.trim();
    Matcher m = yearMonthPattern.matcher(s);
    if (!m.matches()) {
      throw new IllegalArgumentException(
        "Interval string does not match year-month format of 'y-m': " + s);
    } else {
      try {
        int sign = m.group(1) != null && m.group(1).equals("-") ? -1 : 1;
        int years = (int) toLongWithRange("year", m.group(2), 0, Integer.MAX_VALUE);
        int months = (int) toLongWithRange("month", m.group(3), 0, 11);
        result = new CalendarInterval(sign * (years * 12 + months), 0);
      } catch (Exception e) {
        throw new IllegalArgumentException(
          "Error parsing interval year-month string: " + e.getMessage(), e);
      }
    }
    return result;
  }

  /**
   * Parse dayTime string in form: [-]d HH:mm:ss.nnnnnnnnn
   *

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