Does Last 3 rows have the same user id? - php

Question

I'm looking to see if the last 3 rows have the same userId...
I've tried count, select distinct with no luck. Any ideas?
id userId gameId switchId won
--------------------------------
1 1515 5 475 0
2 1515 5 475 0
3 1515 5 475 0
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, FALSE);
$st = $db->prepare("SELECT COUNT(userId) AS total FROM arcadeGamesInPlay WHERE userId=:userid,gameId=:gameId AND switchId=:switchId AND won=:won ORDER by id DESC LIMIT :limit"); // need to filter for next auction
$st->bindParam(':userId', $userId);
$st->bindParam(':gameId', $gameId);
$st->bindParam(':switchId', $switchId);
$st->bindParam(':won', $won);
$st->bindParam(':limit', $limit);
$limit=3;
$won=0;
$st->execute();
$r = $st->fetch(PDO::FETCH_ASSOC);
$playedLastThreeGames= $r['total'];

Answer 1

You need a nested query for this. Imagine a query like this:
SELECT COUNT(DISTINCT userId) FROM arcadeGamesInPlay WHERE id IN (1, 2, 3);
This will return the number of unique userids that were found in the three rows listed - if it returns 1, then you know they're all the same.
You can combine that with a query to select the last three rows. Perhaps something like this:
SELECT id FROM arcadeGamesInPlay ORDER BY id DESC LIMIT 3
...although you may want to add a WHERE clause as well.
Altogether, your query would look like this:
SELECT COUNT(DISTINCT userId)
FROM arcadeGamesInPlay
WHERE id IN (
SELECT id
FROM arcadeGamesInPlay
ORDER BY id DESC
LIMIT 3
);
All that being said, you haven't specified what database you're actually connecting to - and if it's MySQL, you're going to run into problems, because MySQL doesn't support a LIMIT clause on a subquery with the IN operator.
An alternative form of the subquery that will work with MySQL looks like this:
SELECT COUNT(DISTINCT userId)
FROM (
SELECT userId
FROM arcadeGamesInPlay
ORDER BY id DESC
LIMIT 3
) u;
An SQL Fiddle that shows both queries can be seen here: http://sqlfiddle.com/#!2/dda29/4
I've commented out the LIMIT part of the first query so it will work in MySQL. If you change the database engine to something else (PostgreSQL for example), you should be able to uncomment that and have both queries work properly.