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?

ParserToken parser_closing_bracket(TokenType::ClosingRoundBracket);
        if (parser_closing_bracket.ignore(pos, expected))
        {
            node = result;
            return true;
        }
    }
    
    ParserIdentifier parser_parent_window;
    ASTPtr window_name_identifier;
    if (!parser_parent_window.parse(pos, window_name_identifier, expected))
    {
        return false;
    }
    result->parent_window_name = window_name_identifier->as<const ASTIdentifier &>().name();
    if (!parseWindowDefinitionParts(pos, *result, expected))
    {
        return false;
    }
    ParserToken parser_closing_bracket(TokenType::ClosingRoundBracket);
    if (!parser_closing_bracket.ignore(pos, expected))
    {
        return false;
    }
    node = result;
    return true;
}
bool ParserWindowList::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)