Selecting multiple tables MySQL and retrieving different data - php

Question

I have 4 tables that I need to pull data from. I need to count how many people are signed for a single event and see if a user is applied for an event.
These are my table setups:
TABLE: users
+----+----------+-------+--------+-------+
| id | username | level | class | guild |
+----+----------+-------+--------+-------+
| 1 | example1 | 100 | Hunter | blah |
| 2 | example2 | 105 | Mage | blah2 |
| 3 | example3 | 102 | Healer | blah |
+----+----------+-------+--------+-------+
ID is primary
TABLE: event_randoms
+----+----------+-------+--------+----------+----------+
| id | username | level | class | apped_by | event_id |
+----+----------+-------+--------+----------+----------+
| 1 | random1 | 153 | Hunter | 3 | 3 |
| 2 | random2 | 158 | Healer | 3 | 1 |
| 3 | random3 | 167 | Warrior| 1 | 3 |
+----+----------+-------+--------+----------+----------+
ID is primary
apped_by should be foreign key to users.id
event_id should be foreign key to events.id
TABLE: events
+----+------------+------------+-----------+-----------+-----------+
| id | event_name | event_date | initiator | min_level | max_level |
+----+------------+------------+-----------+-----------+-----------+
| 1 | event1 | date1 | 1 | 100 | 120 |
| 2 | event2 | date2 | 1 | 121 | 135 |
| 3 | event3 | date3 | 1 | 100 | 120 |
| 4 | event4 | date4 | 1 | 150 | 200 |
+----+------------+------------+-----------+-----------+-----------+
ID is primary
TABLE: event_apps
+----+----------+--------------+
| id | event_id | applicant_id |
+----+----------+--------------+
| 1 | 3 | 2 |
| 2 | 4 | 2 |
| 3 | 3 | 1 |
| 4 | 1 | 3 |
+----+----------+--------------+
ID is primary
event_id should be foreign key to events.id
applicant_id should be foreign key to users.id
I will be the first to admit that I am very new to this. I just learned how to use MySQL a few days ago. I can grab stuff from a single table, but I am unsure how to grab from multiple tables.
This is the SQL query I tried
SELECT DD_events.id, event_id, applicant_id, guild, level, class, DD_users.id
FROM DD_events, DD_event_apps, DD_users
WHERE DD_event_apps.event_id = DD_events.id
AND DD_event_apps.applicant_id = DD_users.id
and tried to print_r an array but the array turns up empty.
So a few questions pertain to this:
1: How would I count and display as a number how many people (users and randoms) are signed up for an event?
eg: event 3 should have 4 total (2 users and 2 randoms)
2: How do I see if a particular individual is signed for an event and display text based if they are or not?
eg: user 1 is signed up for event 3 so it would be "Registered" but user 2, who is not signed, would display "Not Registered"
3: I want to display info for who is signed for a particular event in 2 tables, 1 for users and another for randoms.
eg: Event 3 would have 2 users info (username, guild, class, level) under the users table and then 2 random users info (name, class, level, what user applied this person) in the random table.
Any and all help is appreciated even if you can answer 1 part.

Answer 1

I'm thinking this would be your base query:
SELECT
event.id,
app.applicant_id,
usr.guild,
usr.level,
usr.class,
usr.id AS Userid
FROM
DD_events event
JOIN
DD_event_apps app
ON (event.id = app.event_id)
LEFT JOIN
DD_users usr
ON (app.user_id = usr.id)
You can make modifications to this to aggregate it, like so:
SELECT
event.id,
COUNT(app.applicant_id) AS ApplicantCount,
COUNT(DISTINCT usr.guild) AS UniqueGuilds,
COUNT(DISTINCT usr.level) AS UniqueLevels,
COUNT(DISTINCT usr.class) AS UniqueClasses,
COUNT(DISTINCT usr.id) AS UniqueUsers
FROM
DD_events event
JOIN
DD_event_apps app
ON (event.id = app.event_id)
LEFT JOIN
DD_users usr
ON (app.user_id = usr.id)
GROUP BY
event.id
I could write those scripts for you, but I think this provides a good starting point for you to continue from. You'll find that T-SQL is fairly simple when you are trying to get the results you are looking for. Hope this helps!

Answer 2

<?php $query = "SELECT count(*) AS numbuh FROM DD_event_apps WHERE event_id = {$row['id']}";
try
{
// These two statements run the query against your database table.
$stmt = $db->prepare($query);
$stmt->execute();
}
catch(PDOException $ex)
{
// Note: On a production website, you should not output $ex->getMessage().
// It may provide an attacker with helpful information about your code.
die("Failed to run query: " . $ex->getMessage());
}
echo($query);
// Finally, we can retrieve all of the found rows into an array using fetchAll
$count = $stmt->fetchAll();
echo($count['numbuh']); ?>