How to traverse a table that has no contiguous fields updated

How do I traverse a table that has no contiguous fields updated?
A MySQL table with the following fields
Id,cs,

The ID is a primary key, but the value is not contiguous
1,3,7,8,9,10,..... This

I need to traverse the Update table, the code is written out, the following query does not know how to loop

PHP Code

  
   Here I have reached the total number of rows for this table $sql      = "SELECT count (*) from". $db _table;                    $exec      = mysql_fetch_array ($con);                    $allgoods = $exec [0]; Total number of rows                                        $sql = "Update". $db _table. "' Set cs = '". Rand ($summin, $summax). "' ";//UPDATE statement

If the ID is sequential.
I think the following statement is possible.

PHP Code

  
   for ($i =0; $i <= $allgoods; $i + +) {$sql = "update". $db _table. "' Set cs= '". Rand ($summin, $summax). "' WHERE id = '". $i. "'"; Query ....}

However, the ID here is not contiguous

How does this work?

------Solution--------------------

PHP Code

$sql = "SELECT id from". $db _table;            $result = mysql_query ($sql, $con);        while ($row =mysql_fetch_object ($result)) {                       $id = $row->id;                    echo $id. "
";                    }
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