MySQL Speed

Can someone tell me which of these 2 SQL queries will be more efficient? I'm
having a debate with another guy about which would be less resource
intensive for MySQL.

The first uses MySQL to pick a random row in a single statement:
<?php
$sql = "SELECT FROM myTable ORDER BY RAND() LIMIT 1";
$query = mysql_query($sql,$conn);
?>


The second does the same thing, but uses 2 queries to do it:
<?php
$sqlA = "SELECT COUNT(id) FROM myTable";
$queryA = mysql_query($sqlA,$conn);
$num = mysql_result($queryA,0,0);
$random = rand(1,$num);
$sqlB = "SELECT FROM myTable WHERE id='" . $random . "' LIMIT 1";
?>

Basically, which approach would be better to use in a high traffic
environment to retrieve a single random row?


Thanks for any help/advice you can give!

ps. the code may not be 100% correct, it is for demonstration purposes only!


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