I tested using "fetch all" versus "while / fetch array" and :fetch-all uses less memory (but not for so much).In my case (test1 and test2): 147008,262848 bytes (fetch-all) versus 147112,262888 bytes (fetch-array & while.So, about the memory, in both cases are the same.However, about the performanceMy test takes :350ms (worst case) using fetch-all, while it takes 464ms (worst case) using fetch-array, or about 35% worst using fetch array and a while cycle.So, using fetch-all, for a normal code that returns a moderate amount of information is :a) cleaner (a single line of code)b) uses less memory (about 0.01% less)c) faster.php 5.6 32bits, windows 8.1 64bits

be careful fetch_all(MYSQLI_ASSOC ) returns an array in the form<?phparray(0 => array(...row...), 1 => array(...row...) .... ), even if is one row...?>not compared to fetch_assoc() which returns one array of the result in form:<?phparray(...row...)?>

By the way, this case pretty work's too:$services = $mysqli->query("SELECT * FROM table1");if($services && $services->num_rows>0){    $services->fetch_all(MYSQLI_ASSOC);}foreach($services as $service){    echo $service; //work properly, cause it implements Iterator  }That's mean in this case $services is a valid array (or empty array)

If you really need this function, you can just extend the mysqli_result class with a function like this one.<?php        public function fetch_all($resulttype = MYSQLI_NUM)        {            if (method_exists('mysqli_result', 'fetch_all')) # Compatibility layer with PHP < 5.3                $res = parent::fetch_all($resulttype);            else                for ($res = array(); $tmp = $this->fetch_array($resulttype);) $res[] = $tmp;            return $res;        }?>

Return value changed in 5.3.3 - between 5.3.0 and 5.3.2 (incl.) when the result set was empty NULL was returned. 5.3.3+ returns an empty array.Also, mysqli_fetch_all works only for buffered result sets, which are the default for mysqli_query. MYSQLI_USE_RESULT will be supported in 5.3.4+However, it makes little sense to use it this way, materialising unbuffered sets. In this case choose STORE_RESULT, and fetch_all won't copy the data, but reference it, as it is stored already in mysqlnd.