presto-base-jdbc/src/main/java/io/prestosql/plugin/jdbc/JdbcColumnHandle.java/JdbcColumnHandle/toString
class JdbcColumnHandle:    @Override
    public String toString()
    {
        return Joiner.on(":").join(
                columnName,
                columnType.getDisplayName(),
                jdbcTypeHandle.getJdbcTypeName());
    }