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?

{
    if (!ParserCompoundIdentifier(true, true).parse(pos, node, expected))
        return false;
    if (pos->type != TokenType::Dot)
        return false;
    ++pos;
    if (pos->type != TokenType::Asterisk)
        return false;
    ++pos;
    auto res = std::make_shared<ASTQualifiedAsterisk>();
    res->children.push_back(node);
    ParserColumnsTransformers transformers_p;
    ASTPtr transformer;
    while (transformers_p.parse(pos, transformer, expected))
    {
        res->children.push_back(transformer);
    }
    node = std::move(res);
    return true;
}
static bool parseColumnsMatcherBody(IParser::Pos & pos, ASTPtr & node, Expected & expected, ParserColumnsTransformers::ColumnTransformers allowed_transformers)