Pros:
- it is convenient to type and read numbers this way;
- Ada, Perl, C++, Go and Rust already support that;
- can support thousands as well as lakhs and crores;

Cons:
- standard SQL does not have this support;
- PostgreSQL treat `SELECT 1_000_000` as number one with `_000_000` alias: http://sqlfiddle.com/#!17/0a28f/400
- C++ has `1'000'000` instead of `1_000_000`;

What do you think?

}
        else
        {
            return false;
        }
        if (keyword_preceding.ignore(pos, expected))
        {
            node->frame_begin_preceding = true;
        }
        else if (keyword_following.ignore(pos, expected))
        {
            node->frame_begin_preceding = false;
            if (node->frame_begin_type == WindowFrame::BoundaryType::Unbounded)
            {
                throw Exception(ErrorCodes::BAD_ARGUMENTS,
                    "Frame start cannot be UNBOUNDED FOLLOWING");
            }
        }
        else
        {
            return false;
        }
    }
    if (has_frame_end)
    {
        if (!keyword_and.ignore(pos, expected))
        {
            return false;
        }
        if (keyword_current_row.ignore(pos, expected))