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?

{
    ParserIdentifier non_parametric;
    ParserIdentifierWithParameters parametric;
    if (parametric.parse(pos, node, expected))
    {
        auto * func = node->as<ASTFunction>();
        func->no_empty_args = true;
        return true;
    }
    ASTPtr ident;
    if (non_parametric.parse(pos, ident, expected))
    {
        auto func = std::make_shared<ASTFunction>();
        tryGetIdentifierNameInto(ident, func->name);
        func->no_empty_args = true;
        node = func;
        return true;
    }
    return false;
}
bool ParserAssignment::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)