How to display the highest value per column using data from a table?

Question

My table looks like this. This is my code to display the average per category. But I want to find the highest value per column. Like in C1.1 I want find the highest average value in that column.

<div class="container" class="col-lg-5">
<table class="table table-striped table table-bordered" >
<tr><th>Campus</th>
<th>No. of Staff</th>
<th>C1.1</th>
<th>C1.2</th>
<th>C1.3</th>
<th>C1.4</th>
<th>C1.5</th>
<th>C1.6</th>
<th>C2.1</th>
<th>C2.2</th>
<th>C2.3</th>
<th>C3.1</th>
<th>C3.2</th>
<th>C3.3</th>
<th>C3.4</th>

    <tr>
    <td>MAIN 1 - CABEIHM</td>
    <td>
            <?php   
            $queryn ="SELECT COUNT(dept_code) FROM employment where                                     dept_code=3 and empg_code=1";
            $resultn = mysql_query($queryn) or die(mysql_error());
            while($row1 = mysql_fetch_array($resultn)){
            echo "".$row1['COUNT(dept_code)'];
             echo "<br />";
             }
         ?>
    </td>
    <td><!--1.1-->
    <?php

    $query1 = ("SELECT  ROUND(AVG(Compv11),2) , dept_code ,  camp_code
                                FROM performance 
                                INNER JOIN employment 
                                ON employment.emp_code=performance.emp_id AND employment.dept_code=performance.dept_id
                                WHERE empg_code=1  AND dept_id=3
                                ");
                $result1 = mysql_query($query1) or die(mysql_error());
            [enter image description here][1]

                // Print out result
                while($row = mysql_fetch_array($result1))
                {
                echo "".$row['ROUND(AVG(Compv11),2)'];
                }

        ?>

Answer 1

To get the row with the highest average value from the C1.1 column, your best option is to calculate this in PHP.

You are currently outputting the values directly as soon as you get them from the database. You'll need to store the average values in a variable, so you can get the highest value later:

$averages = array();

$query1 = ("SELECT  ROUND(AVG(Compv11),2) , dept_code ,  camp_code
            FROM performance 
            INNER JOIN employment 
            ON employment.emp_code=performance.emp_id AND employment.dept_code=performance.dept_id
            WHERE empg_code=1  AND dept_id=3
");

$result1 = mysql_query($query1) or die(mysql_error());

// Print out result
while($row = mysql_fetch_array($result1))
{
    $averages[1] = $row['ROUND(AVG(Compv11),2)'];
    echo "".$row['ROUND(AVG(Compv11),2)'];
}

Note that I'm adding the result to index 1 of $averages , because your variables are called $query1 and $result1 and I assume that for all your other rows you use incrementing variables (ie $query2 and $result2 for the second row, etc.). What follows is not very efficient, I'll give you an alternative afterwards.

Once you have all the average values in $averages , you can sort the array:

arsort($averages);

This will sort the array in reverse order (meaning the first entry will be the one with the highest value) while keeping the index to value association. Now we reset() the array to be safe, after which you can get the index using the key() function and the value itself using the current() function:

reset($averages);
$highest_index = key($averages);
$highest_value = current($averages);

$highest_query = "query" . $highest_index;
$highest_result = "result" . $highest_index;

Now you know that the highest value came from $$highest_query and its result is in $$highest_result , in case you want to do something with that information. You can, for example, use mysql_data_seek($$highest_result, 0) to reset it and then you can fetch its row again using mysql_fetch_array($$highest_result) .

Although you should really consider moving away from the old, unsupported, mysql_* functions and toward mysqli or PDO for your database communication.

Now for that alternative I mentioned:

Depending on what you want to do with the highest value (you say you want to output it and "make a report on it"), you probably also want to know which empg_code and dept_id you're filtering on in your query, or the dept_code or camp_code you're selecting along with the average value.

So let's fill our $averages array with more than just the average values:

while($row = mysql_fetch_array($result1))
{
    $averages[] = array(
        'avg' => $row['ROUND(AVG(Compv11),2)'],
        'empg_code' => 1,
        'dept_id' => 3,
        'dept_code' => $row['dept_code'],
        'camp_code' => $row['camp_code']
    );
    echo "".$row['ROUND(AVG(Compv11),2)'];
}

Now we can use usort to sort the array using a custom function:

usort($averages, function($a, $b) {
    if ($a['avg'] == $b['avg']) {
        return 0;
    }

    // note: reverse check of the example, because we want to
    // sort in DESCENDING order
    // https://php.net/usort
    return ($a['avg'] > $b['avg']) ? -1 : 1;
});

Now the data for the entry with the highest value will be the first entry of the $averages array:

$highest = $averages[0];

echo $highest['avg'];       // highest average value
echo $highest['empg_code']; // 1
echo $highest['dept_id'];   // 3
echo $highest['dept_code']; // dept_code for the highest average value
echo $highest['camp_code']; // camp_code for the highest average value

Hope that helps!