PHP MySQL Query - php

Question

Currently I have 3 MySQL tables, one filed with the users information, one with their course history and the last one filled with their reward history.
I am attempting to create a "rewards" program if you will, using these two databases and a PHP script. As far as the reward requirements, I have 2 arrays setup for the two types of rewards:
//Pen Reward with course A & B required
$pen=array("a","b")
//Cup Reward with course B & C required
$cup=array("b","c")
I can't figure out how to first query for all user IDs, then go through their history. If they match the requirements set above, then to update the reward table to 1 (to show that they received the award)
UsersDB
userid name
----------------
1 bill
2 john
3 steve
HistoryDB
userid courseid
------------------
1 a
1 b
2 b
3 a
3 c
RewardHistoryDB
userid pen cup
---------------------
1 0 0
2 0 0
3 0 0
Ideally it after the PHP script runs, it would update the RewardHistoryDB to reflect that user 1 received a pen, and user 3 received a cup.(the DB would look like this:)
RewardHistoryDB (after)
userid pen cup
---------------------
1 1 0
2 0 0
3 0 1
Here is the PHP code I am using right now (not complete):
$userid=array();
$i=0;
//Find All users
$result = mysqli_query($con,"SELECT userid FROM usersdb")
while ($row = mysqli_fetch_array($result)){
$universityid[$i]=$row['universityid'];
$i++;
}
//Find History
$courseid=array();
foreach ($userid as $userid1){
$result = mysqli_query($con,"SELECT courseid FROM historydb WHERE userid='".$userid1."'");
while ($row = mysqli_fetch_array($result)){
$courseid[]=$row;
}
}
//Update Reward DB
//Don't even know where to start...
Any help would be greatly appreciated.
If you have any questions, please let me know.
Thank you in advanced!

Answer 1

http://sqlfiddle.com/#!2/1a96b/1/0
You can do this just as queries and without doing any logic in PHP
update RewardHistoryDB
set Pen = 1
where UserID in (
select UserID
from HistoryDB
where CourseID in ('A','B')
group by UserID
having count(UserID)=2);
update RewardHistoryDB
set Cup = 1
where UserID in (
select UserID
from HistoryDB
where CourseID in ('B','C')
group by UserID
having count(UserID)=2);
Or you can even do it in one, large statement...
update RewardHistoryDB
left outer join (
select UserID as Pens_UserID
from HistoryDB
where CourseID in ('A','B')
group by UserID
having count(UserID)=2 ) as Pens
on RewardHistoryDB.UserID = Pens.Pens_UserID
left outer join (
select UserID as Cups_UserID
from HistoryDB
where CourseID in ('B','C')
group by UserID
having count(UserID)=2 ) as Cups
on RewardHistoryDB.UserID = Cups.Cups_UserID
set Pen = case when Pens.Pens_UserID is not null then 1 else 0 end,
Cup = case when Cups.Cups_UserID is not null then 1 else 0 end