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?

{
        ++pos;
    }
    IParser::Pos literal_begin;
    Collection arr;
};
template <typename Collection>
bool ParserCollectionOfLiterals<Collection>::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    if (pos->type != opening_bracket)
        return false;
    std::vector<CollectionOfLiteralsLayer<Collection>> layers;
    layers.emplace_back(pos);
    pos.increaseDepth();
    ParserLiteral literal_p;
    while (pos.isValid())
    {
        if (!layers.back().arr.empty())
        {
            if (pos->type == closing_bracket)
            {
                std::shared_ptr<ASTLiteral> literal;