如何在索引不匹配时比较两个数组

Question

I've got two mySQL queries which pull data from my database. Without going into too much detail, after running the queries the results of both should be related when assigning to an array (i.e. array1[x] and array2[x] should be related by the x offset by virtue of the nature of the sql queries).

However this isn't robust enough if something happens where one of the queries returns less or more than the other, then the offset will be off making my for loop comparison (at the end of the code snippet below) faulty.

['companyid'] in both arrays is fixed and will not change, so is there a way of making that the index of the arrays and looping through it for comparison instead? Note that ['companyid'] can be any non-sequential number.

*SQL Query*

         while ($row = $result->fetch()) {  
            $pastcompanies[] = array(
                    'companyid' => $row['id'],
                    'name' => $row['name'],
                    'contactid' => $row['contactid'],
                    'firstname' => $row['firstname'],
                    'lastname' => $row['lastname'],
                    'email' => $row['email']        
   );
        }   

*SQL Query*

         while ($row = $result->fetch()) {  
            $nowcompanies[] = array(
                    'companyid' => $row['id'],
                    'name' => $row['name'],
                    'contactid' => $row['contactid'],
                    'firstname' => $row['firstname'],
                    'lastname' => $row['lastname'],
                    'email' => $row['email']        
    );
        }   

        for ($x=0;$x<count($pastcompanies);$x++){
                if ($pastcompanies[$x]['contactid']!=$nowcompanies[$x]['contactid']){
                     echo $pastcompanies[$x]['firstname']." has been replaced by "
                     .$nowcompanies[$x]['firstname']; 
                }
        }       

Answer 1

Comparison on array is slow, unnecessary and insecure compared to a database query doing the comparison. A query using join to compare two tables is more robust.

SELECT * FROM companies c
JOIN past_companies pc 
ON pc.companyid = c.companyid
WHERE pc.contactid != c.contactid;

This code above should give you a result set where all the first names aren't the same as before. Thus eliminating the need to compare arrays on php. Please not that this code is just a sample to how a comparison can be done on the database.