php - Random row selection using MySQL returns NULL -


i trying random row mysql table 3 attemps:

$query = "select cid table limit 1 offset ".rand(1,$num_rows); $query = "select cid table offset random() * (select count(*) table) limit 1"; $query = "select * table order rand() limit 1";


give null result in mysql_query($query).

higher php code obtain row same table ok specifying where, don't understand why can't retrieve random one.

here code snippet:

    $query = "select uid,clu uable un = '$un'";     $result = mysql_query($query) or die(sqlerror(__line__,mysql_errno(),mysql_error()));     $resultid = mysql_fetch_assoc($result);     $uid = $resultid['uid']; file_put_contents('debugging.txt',__line__.' - $uid = '.var_export($uid,true).php_eol,file_append);     $query = "select * table uid = $uid , cn = '$cn'";     $result = mysql_query($query) or die(sqlerror(__line__,mysql_errno(),mysql_error()));     $cr = mysql_fetch_assoc($result);     $cid= $cr['cid']; file_put_contents('debugging.txt',__line__.' - $cid= '.var_export($cid,true).php_eol,file_append);     $query = "select * fable cid= '$cid'";     $result = mysql_query($query) or die(sqlerror(__line__,mysql_errno(),mysql_error())); file_put_contents('debugging.txt',__line__.' - $result = '.var_export($result,true).php_eol,file_append);     $fr = mysql_fetch_assoc($result); file_put_contents('debugging.txt',__line__.' - $fr = '.var_export($fr,true).php_eol,file_append);     echo  '<form action="'.$_server['php_self'].’" method="post">';     if (!$fr) {         $o= $cn;         while ($o= $cn) { //    $ac = mysql_query("select * table") or die(sqlerror(__line__,mysql_errno(),mysql_error())); //    $num_rows = mysql_num_rows($ac); //file_put_contents('debugging.txt',__line__.' - $num_rows = '.$num_rows.php_eol,file_append); //    --$num_rows; //    $query = "select cid table limit 1 offset ".rand(1,$num_rows);     $query = "select cid table offset random() * (select count(*) table) limit 1"; //        $query = "select * table order rand() limit 1";         $resultid = mysql_query($query) or die(sqlerror(__line__,mysql_errno(),mysql_error()));         $opr = mysql_fetch_assoc($resultid);         $o= $opr['cn'];         } file_put_contents('debugging.txt',__line__.' - $query = '.$query.php_eol,file_append); file_put_contents('debugging.txt',__line__.' - $resultid = '.var_export($resultid,true).php_eol,file_append); file_put_contents('debugging.txt',__line__.' - $op[\'cid\'] = '.$op['cid'].php_eol,file_append);         $query = "select * table cid= ".$op;         $result = mysql_query($query) or die(sqlerror(__line__,mysql_errno(),mysql_error()));         $opr = mysql_fetch_assoc($opr);         $o= $opr['cn'];         $od= $opr['description'];         echo  '<p>'.$op;         if ($od<> '') {         echo  ','.$odesc;         }         echo  '</p>';         echo  '<input type="submit" name="continue" id="continue" value="continue">';     } else {         echo  '<p>'.$fr['p'].'</p>';         echo  '<input type="submit" name="continue" id="continue" value="continue">';     }     echo  '</form>';

the resulting debugging.txt:
24 - $uid = '4'
29 - $cid = '21'
32 - $result = null
34 - $fr = false

these queries ok, think you're starting @ wrong place. when you're uncertain how frame in sql, open sql client sequelpro or navicat , try writing few queries hand until result want. (also gives chance double-check contents of relevant tables , ensure expected data there.) can go php full confidence sql code correct, if there's problem must php (either variables inject mysql statement, or way call statement).


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