apache/seatunnel · warning

Skipping unsupported default value for column

Error message

Skipping unsupported default value for column {} in table {}. Using NULL constraint instead.

What it means

During schema evolution on a DM (Dameng) database, when a column has a default value written in a 'special' dialect-specific form (e.g. expression/current-timestamp defaults from the source dialect) that DM cannot represent, DmdbDialect.applySchemaChange skips the default value and appends only a NULL constraint, logging this warning. The column is added but without the original default, so inserts that relied on it may fail or produce different values.

Solutions

1. Add the column manually on DM with a DM-compatible DEFAULT (e.g. CURRENT_TIMESTAMP) before the event arrives
2. Change the source column default to a portable literal both dialects support
3. Make the column nullable without a default and set values in application code / a transform
4. Extend/patch isSpecialDefaultValue handling in the DM dialect to translate the specific default expression

Example fix

// before (source DDL, MySQL)
ALTER TABLE t ADD COLUMN updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP(6);
// after (DM-compatible default)
ALTER TABLE t ADD COLUMN updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP NULL;

// before applying schema change on DM
Column col = event.getColumn();
if (col.getDefaultValue() != null
        && isSpecialDefaultValue(col.getDefaultValue(), sourceDialectName)) {
    throw new IllegalArgumentException("Column " + col.getName()
        + " uses a default value unsupported by DM; add it manually with a DM-compatible DEFAULT");
}

boolean hasPortableDefault(Column col) {
    String d = col.getDefaultValue();
    return d == null || !isSpecialDefaultValue(d, sourceDialectName);
}

When it happens

Trigger: applySchemaChange builds ADD COLUMN DDL where column.getDefaultValue() != null and isSpecialDefaultValue(defaultValue, sourceDialectName) is true, and the column ends up on the nullable branch (so instead of embedding the unsupported default, it emits 'NULL').

Common situations: Cross-database schema sync (e.g. MySQL -> DM) where source defaults like CURRENT_TIMESTAMP(6), expression defaults, or driver-specific literals have no DM equivalent; schema evolution events carrying computed default values.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Default value is not supported for column
• Skipping unsupported default value for column
• Skipping unsupported default value for column
• Column already exists in table . Skipping add column…
• Column already exists in table . Skipping change column…

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/5c62ab8f9282abb8. Report an issue: GitHub.

Appendix: source

Thrown at seatunnel-connectors-v2/connector-jdbc/src/main/java/org/apache/seatunnel/connectors/seatunnel/jdbc/internal/dialect/dm/DmdbDialect.java:245

                        .append(" ADD ")
                        .append(quoteIdentifier(column.getName()))
                        .append(" ")
                        .append(columnType);

        if (column.getDefaultValue() != null
                && !column.isNullable()
                && (sameCatalog
                        || !isSpecialDefaultValue(
                                typeDefine.getDefaultValue(), sourceDialectName))) {
            // Handle default values and null constraints
            String defaultValueClause = sqlClauseWithDefaultValue(typeDefine, sourceDialectName);
            sqlBuilder.append(" NOT NULL ").append(defaultValueClause);
        } else {
            // If the column is nullable or the default value is not supported,
            // the NULL constraint is added.
            if (column.getDefaultValue() != null
                    && isSpecialDefaultValue(typeDefine.getDefaultValue(), sourceDialectName)) {
                log.warn(
                        "Skipping unsupported default value for column {} in table {}. Using NULL constraint instead.",
                        column.getName(),
                        tablePath.getFullName());
            }
            sqlBuilder.append(" NULL");
        }
        ddlSQL.add(sqlBuilder.toString());

        // Process column comment
        if (column.getComment() != null) {
            ddlSQL.add(buildColumnCommentSQL(tablePath, column));
        }

        // Execute the DDL statement
        executeDDL(connection, ddlSQL);
    }

    @Override

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