Please look at this code there is wrong, run the result of the dead loop

Ask tall man to see this piece of code there is wrong, run the result of the dead loop.
$result =mysql_query ("select * FROM St WHERE cid = 1");
$max _num=mysql_num_rows ($result);//Gets the number of records in the database
Srand (Double) microtime () *10000000); Generates a random number seed.


$se _pos=rand (0, $max _num-1); Random number from 0 to maximum record count
$length = 1; Set the number of records to be taken together
The following is the removal of the specified number of records.
$result _lim=mysql_query ("select * FROM St WHERE cid = 1 limit $se _pos, $length");
$myrow _lim=mysql_fetch_array ($result _lim);


$se _pos1=rand (0, $max _num-1);
$result _lim1=mysql_query ("select * FROM St WHERE cid = 1 limit $se _pos1, $length");
$myrow _lim1=mysql_fetch_array ($result _lim1);


while ($myrow _lim= $myrow _lim1) {
$se _pos1=rand (0, $max _num-1);
$result _lim1=mysql_query ("select * FROM St WHERE cid = 1 limit $se _pos1, $length");
$myrow _lim1=mysql_fetch_array ($result _lim1);
}


------to solve the idea----------------------
$result _lim1=mysql_query ("select * FROM St WHERE cid = 1 limit $se _pos1, $length"); Always return a result set containing at least one record, unless an error occurs
$myrow _lim1=mysql_fetch_array ($result _lim1);//So $myrow _lim1 is always a non-empty array

Since $myrow _lim1 is not empty, how can this cycle end?
while ($myrow _lim= $myrow _lim1) {

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