void appendOnDuplicateClause(StringBuilder sb) {
        sb.append("ON DUPLICATE KEY UPDATE ");
        Iterator<String> it = jdbcTable.dbFieldNames().iterator();
        while (it.hasNext()) {
            String dbFieldName = it.next();
            dialect.quoteIdentifier(sb, dbFieldName);
            sb.append(" = VALUES(");
            dialect.quoteIdentifier(sb, dbFieldName);
            sb.append(')');
            if (it.hasNext()) {
                sb.append(',');
            }
        }
    }
@Test
    void appendOnDuplicateClause() {
        MySQLUpsertQueryBuilder builder = new MySQLUpsertQueryBuilder(jdbcTable, dialect);
        StringBuilder sb = new StringBuilder();
        builder.appendOnDuplicateClause(sb);

        String valuesClause = sb.toString();
        assertThat(valuesClause).isEqualTo(
                "ON DUPLICATE KEY UPDATE " +
                        "`field1` = VALUES(`field1`)," +
                        "`field2` = VALUES(`field2`)");
    }