如何使用PHP和MySQL根据表中的搜索值更新数据

I need one help.I need to update column value with one data,If that is not present in that column using PHP and MySQL. I am explaining my table below.

db_special:

 id      name       special  
 1       aaa         1
 2       bbb         6
 3       ccc         1,7
 4      ddd          1,6,7
 5      eee            1

Here my condition is little bit complex. I need to update 7 with comma separated to those row which has not value like 7 and 6. As per my condition the table should looks like below after update.

 1      aaa        1,7    
 2      bbb         6    
 3      ccc        1,7    
 4      ddd        1,6,7    
 5      eee        1,7

Here as per condition only first and last rows are reflecting. I need query for this so that I can get result as per expected.Please help.

You can do like as below:

$select = "SELECT special FROM db_special" //select data

while($result) { // go through each loop
    $special = explode(",", $result['special']) ;
    if(!in_array(7, $special) && !in_array(6, $special)) {
        $special_new = (!empty($result['special'])) ? $result['special'].", 7" : "7";
        $query = update db_special SET special = $special_new //update data
    }
}