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

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

{
    ASTFunction * function = dynamic_cast<ASTFunction *>(node.get());
    
    
    
    
    
    if (pos->type != TokenType::OpeningRoundBracket)
    {
        ASTPtr window_name_ast;
        ParserIdentifier window_name_parser;
        if (window_name_parser.parse(pos, window_name_ast, expected))
        {
            function->children.push_back(window_name_ast);
            function->window_name = window_name_ast;
            return true;
        }
        else
        {
            return false;
        }
    }
    ++pos;
    
    
    ParserKeyword keyword_partition_by("PARTITION BY");
    ParserNotEmptyExpressionList columns_partition_by(
        false );
    ParserKeyword keyword_order_by("ORDER BY");