mysql_num_rows是否有效和/或标准实践？

Question

A while ago I was poking around with SQLite, trying to port some of my sites to use it instead of MySQL. I got hung up on the lack of a function to count results, like PHP's mysql_num_rows(). After searching a little I discovered this mail list, which says (as I understand it) that SQLite doesn't have that functionality because it's inefficient. It states that it is bad form to write code that needs to know how many rows are returned.

I generally use mysql_num_rows to check for empty return results. For example:

$query = "SELECT * FROM table WHERE thing = 'whatever'";
$results = mysql_query($query);

if (mysql_num_rows($results)) {
    while ($row = mysql_fetch_array($results)) {
        echo "<p>$row[whatever]</p>";
    }
} else {
    echo "<p>No results found</p>";
}

The vehement distaste for the concept of mysql_num_rows() in the SQLite community makes me wonder if it's that terribly efficient for regular MySQL in PHP.

Is there a better, more accepted way for checking the size of a MySQL result set in PHP besides mysql_num_rows()?

EDIT: I'm not just using mysql_num_rows to get the count--I would use a COUNT query for that. I'm using it to check if there are any results before outputting everything. This is useful for something like displaying search results - it's not always guaranteed that there will be results. In SQLite world, I have to send one COUNT query, check if there is something, and then send a SELECT query to get everything.

Answer 1

You already have something that is telling you if you've got results in mysql_fetch_array(). It returns false if there are no more rows to fetch (from php.net).

$query = "SELECT * FROM table WHERE thing = 'whatever'";
$results = mysql_query($query);
if($results) {
    $row = mysql_fetch_array($results);
    if($row) {
        do {
            echo "<p>{$row[whatever]}</p>";
        } while($row = mysql_fetch_array($results));
    } else {
        echo "<p>No results found</p>";
    }

} else {
    echo "<p>There was an error executing this query.</p>";
}