(no version information, might be only in CVS)
PDOStatement::fetchAll -- 
     Returns an array containing all of the result set rows
    
返回值
     PDOStatement::fetchAll() returns an array containing
     all of the remaining rows in the result set. The array represents each
     row as either an array of column values or an object with properties
     corresponding to each column name.
    
     Using this method to fetch large result sets will result in a heavy
     demand on system and possibly network resources. Rather than retrieving
     all of the data and manipulating it in PHP, consider using the database
     server to manipulate the result sets. For example, use the WHERE and
     SORT BY clauses in SQL to restrict results before retrieving and
     processing them with PHP.