Question

I have a web page where people are able to post a single number between 0 and 10.

There is like a lotto single number generation once daily. I want my PHP script to check on the the posted numbers of all the users and assign a score of +1 or -1 to the relative winners (or losers).

The problem is that once I query the DB for the list of the winning users, I want to update their “score” field (in “users” table). I was thinking of a loop like this (pseudocode)

foreach winner{
    update score +1
}

but this would mean that if there are 100 winners, then there will be 100 queries. Is there a way to do some sort of batch inserting with one single query?

Thanks in advance.

Answer 1

Let’s just assume we have a datatable named posts and users.
Obviously, users contain the data of the gambler (with a convenient id field and points for the number of points they have), and posts contain the post_id ID field for the row, user_id, which is the ID of the user and value, the posted number itself.

Now you only need to implement the following SQL queries into your script:

UPDATE users INNER JOIN posts ON users.id = posts.user_id SET users.points = (users.points + 1)
WHERE posts.value = 0;

Where 0 at the end is to be replaced with the randomly drawn number.

What will this query do? With the INNER JOIN construct, it will create a link between the two tables. Automatically, if posts.value matches our number, it will link posts.user_id to users.id, knowing which user has to get his/her points modified. If someone gambled 0, and his ID (posts.user_id) is 8170, the points field will update for the user having user.id = 8170.

If you alter the query to make it (users.points - 1) and WHERE posts.value != 0, you will get the non-winners having one point deducted. It can be tweaked as much as you want.

Just be careful! After each daily draw, the posts table needs to be truncated or archived.

Another option would be storing the timestamp (time() in PHP) of the user betting the number, and when executing, checking against the stored timestamp… whether it is in between the beginning and the end of the current day or not.

Just a tip: you can use graphical database software (like Microsoft Access or LibreOffice Base) to have your JOINs and such simulated on a graphical display. It makes modelling such questions a lot easier for beginners. If you don’t want desktop-installed software, trying out an installation of phpMyAdmin is another solution too.

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Edit:

Non-relational databases

If you are to use non-relational databases, you will first need to fetch all the winner IDs with:

SELECT user_id FROM posts WHERE value=0;

This will give you a result of multiple rows. Now, you will need to go through this result, one-by-one, and executing the following query:

UPDATE users SET points=(users.points + 1) WHERE id=1;

(0 is the drawn winning number, 1 is the concurrent id of the user to update.)

Without using the relation capabilities of MySQL, but using a MySQL database, the script would look like this:

<?php
$number = 0; // This is the winning number we have drawn

$result = mysql_query("SELECT user_id FROM posts WHERE number=" .$number);

while ( $row = mysql_fetch_assoc($result) )
{
    $curpoints_result = mysql_query("SELECT points FROM users WHERE user_id=" .$row['user_id']);
    $current_points = mysql_fetch_assoc($curpoints_results);

    mysql_query("UPDATE users SET points=" .($current_points['points'] + 1). " WHERE user_id=" .$row['user_id']);
}
?>

The while construct make this loop to run until every row of the result (list of winners) is updated.

Oh and: I know MySQL is a relational database, but it is just what it is: an example.