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?

"GROUP",
    "HAVING",
    "ILIKE",
    "INNER",
    "INTO",
    "JOIN",
    "LEFT",
    "LIKE",
    "LIMIT",
    "NOT",
    "OFFSET",
    "ON",
    "ONLY", 
    "ORDER",
    "PREWHERE",
    "RIGHT",
    "SAMPLE",
    "SEMI",
    "SETTINGS",
    "UNION",
    "USING",
    "WHERE",
    "WINDOW",
    "WITH",
    "INTERSECT",
    "EXCEPT",
    "ELSE",
    nullptr
};
bool ParserAlias::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)