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?

}
    ParserKeyword s_uuid("UUID");
    UUID uuid = UUIDHelpers::Nil;
    if (table_name_with_optional_uuid)
    {
        if (parts.size() > 2)
            return false;
        if (s_uuid.ignore(pos, expected))
        {
            ParserStringLiteral uuid_p;
            ASTPtr ast_uuid;
            if (!uuid_p.parse(pos, ast_uuid, expected))
                return false;
            uuid = parseFromString<UUID>(ast_uuid->as<ASTLiteral>()->value.get<String>());
        }
        if (parts.size() == 1) node = std::make_shared<ASTTableIdentifier>(parts[0], std::move(params));
        else node = std::make_shared<ASTTableIdentifier>(parts[0], parts[1], std::move(params));
        node->as<ASTTableIdentifier>()->uuid = uuid;
    }
    else
        node = std::make_shared<ASTIdentifier>(std::move(parts), false, std::move(params));
    return true;
}
ASTPtr createFunctionCast(const ASTPtr & expr_ast, const ASTPtr & type_ast)
{
    
    auto type_literal = std::make_shared<ASTLiteral>(queryToString(type_ast));
    return makeASTFunction("CAST", expr_ast, std::move(type_literal));
}
bool ParserFilterClause::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)