如何获取一组mysql记录的平均值？

Question

I have a table with a set of fields. Each of these fields contains a number between one and 10.

|item_id|field1|field2|field3|field4|
|1      | 2    |5     |2     |9     |
|3      | 9    |3     |5     |10    |
|4      | 9    |9     |9     |10    |

What I would like to do is get the average of these fields. However, I need the number to be between 10 and 100.

Answer 1

First what you wanna do is multiply the rating by 10;

foreach ($results as $result) {
    $rating = 0;
    $rating = $rating + $result['field1']         + $result['field2'] + $result['field3'] + $result['field4'];

    // Multiply rating by 10
    $rating = $rating*10;

    // Devide rating by 4
    $rating = $rating/4;

    // Output average
    echo $result['item_id']." : ".$rating."<br />";
}

Or you could do it even simpler while doing your query:

SELECT
(field1 + field2 + field3 + field4)*10/4 AS average
FROM table