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?

Expected & expected)
{
    ParserKeyword keyword_rows("ROWS");
    ParserKeyword keyword_groups("GROUPS");
    ParserKeyword keyword_range("RANGE");
    node->frame_is_default = false;
    if (keyword_rows.ignore(pos, expected))
    {
        node->frame_type = WindowFrame::FrameType::ROWS;
    }
    else if (keyword_groups.ignore(pos, expected))
    {
        node->frame_type = WindowFrame::FrameType::GROUPS;
    }
    else if (keyword_range.ignore(pos, expected))
    {
        node->frame_type = WindowFrame::FrameType::RANGE;
    }
    else
    {