MysqlErrorCodeWithRx.java

    @Override
    public void start(Future<Void> fut) {
        jdbcClient = JDBCClient.createShared(vertx, new JsonObject()
            .put("url", "jdbc:mysql://localhost:3306/data")
            .put("driver_class", "com.mysql.cj.jdbc.Driver")
            .put("user", "user")
            .put("password", "secret")
            .put("max_pool_size", 30));

        Json.prettyMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

        jdbcClient.rxGetConnection()
            .flatMap(connection -> connection
                .rxExecute("create table crime(id int primary key, name varchar, villain varchar, wiki varchar)")
                .flatMap(v ->
                    connection.rxExecute("insert into crime values(1, 'Moon', 'Gru', 'https://en.wikipedia" +
                        ".org/wiki/Moon'), "
                        + "(2, 'Times Square JumboTron', 'Gru', 'https://en.wikipedia.org/wiki/One_Times_Square'), "
                        + "(3, 'Kryptonite', 'Lex Luthor', 'https://en.wikipedia.org/wiki/Kryptonite')"
                    )
                )
                .doAfterTerminate(connection::close))
            .subscribe(
                server -> {
                    System.out.println("Done !");
                    fut.complete();
                },
                error -> {
                    System.out.println("Error while connecting to the database");
                    if (error instanceof SQLSyntaxErrorException) {
                          System.out.println("Error code: " + ((SQLSyntaxErrorException) error).getErrorCode());
                    }
                    fut.fail(error);
                });
    }

matching the instance of error with SQLNonTransientException would be better.