**Use case**
`SELECT POSITION('/' IN s) FROM (SELECT 'Hello/World' AS s);`

The same as `position(s, '/')`

{
    if (!ParserKeyword("EXTRACT").ignore(pos, expected))
        return false;
    if (pos->type != TokenType::OpeningRoundBracket)
        return false;
    ++pos;
    ASTPtr expr;
    IntervalKind interval_kind;
    if (!parseIntervalKind(pos, expected, interval_kind))
        return false;
    ParserKeyword s_from("FROM");
    if (!s_from.ignore(pos, expected))
        return false;
    ParserExpression elem_parser;
    if (!elem_parser.parse(pos, expr, expected))
        return false;
    if (pos->type != TokenType::ClosingRoundBracket)
        return false;
    ++pos;
    auto function = std::make_shared<ASTFunction>();
    auto exp_list = std::make_shared<ASTExpressionList>();
    function->name = interval_kind.toNameOfFunctionExtractTimePart();
    function->arguments = exp_list;
    function->children.push_back(exp_list);
    exp_list->children.push_back(expr);
    node = function;
    return true;
}
bool ParserDateAddExpression::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)