SQL order by datetime - php

Question

I have 3 tables:
chatmsgs with the columns
itemid, sender, receiver, message, datetime, status
users with the columns
userid, username, phone, email, avatar, online, password
items with the columns
itemid, category, make, type, mainimage, title, price
I am trying to create a list of chats between the current user and some other user on a specific item and order the list by the chat with the most recent message (based on timestamp).
My current query is this:
<?php
$currentuser=$_SESSION['userid'];
$sqls="SELECT DISTINCT itemid,sender,receiver FROM chatmsgs ORDER BY datetime DESC";
$results=mysqli_query($db,$sqls);
while($rows=mysqli_fetch_assoc($results)){
$itemid=$rows['itemid']; $sender=$rows['sender']; $receiver=$rows['receiver']; #$message=$rows['message'];
$sqll="SELECT * FROM items WHERE itemid = '".$itemid."'";
$resultt=mysqli_query($db,$sqll);
while($roww=mysqli_fetch_assoc($resultt)){
$itemid=$roww['itemid']; $title=$roww['title']; $status=$roww['status']; $userid=$roww['userid'];
#$sqlx = "SELECT * FROM users WHERE userid = '".$userid."' AND userid != '".$currentuser."'";
$sqlx = "SELECT * FROM users WHERE userid = '".$userid."'";
$resultx=mysqli_query($db,$sqlx);
while($rowx=mysqli_fetch_assoc($resultx)){
$avatar=$rowx['avatar']; $username=$rowx['username']; $user=$rowx['userid'];
$sq="SELECT * FROM chatmsgs WHERE itemid = '".$itemid."' AND ((sender = '".$sender."' AND receiver = '".$receiver."') OR (sender = '".$receiver."' AND receiver = '".$sender."')) ORDER BY id ASC";
$resul=mysqli_query($db,$sq);
while($ro=mysqli_fetch_assoc($resul)){
$message=$ro['message'];
$ldate=date_format(date_create($ro['datetime']),"M d");
}
echo '
<li>
My list item
</li>
';
}
}
}
?>
I have so far been able to list the chats but I'm unable to sort it.
I know this is not the best way to do this but it's the only way I know how. Would appreciate better ways.

Answer 1

I would start by getting all chat messages associated with just the given user in question. By doing a UNION as both the sender and receiver, if you have an index on each column respectively, the query should be very fast. From that, you can now query the rest of the data all in one quick run something like below.
You can order the data by whatever... From your while loops, it looked like you were doing all things for a given Item ID before moving to the next, so I have the order by clause by the item ID. Now, from within each item, I have ordered by the date/time in descending order with newest chat message first, but you could change that.
Another possible change is you may want the items displayed based on which is the MOST RECENT item that has chat activity first. For example, if a chat from someone was from a year ago, vs one that was just this week, you might want the current first. I would alter the query slightly.
select
um.itemid,
cm.message,
cm.datetime,
cm.status,
uFrom.username senderName,
uFrom.avatar senderAvatar,
uTo.userName receiptName,
uTo.avatar receiptAvatar,
i.category,
i.make,
i.type,
i.mainImage,
i.title,
i.price
from
( select distinct itemid
from chatMsgs
where sender = $currentuser
UNION
select distinct itemid
from chatMsgs
where receiver = $currentuser ) UM
JOIN ChatMsgs ch
on UM.ItemID = ch.ItemID
JOIN Users uFrom
on ch.sender = uFrom.userid
JOIN Users uTo
on ch.receiver = uTo.userid
JOIN Items i
on ch.itemID = i.itemid
order by
um.itemid,
cm.datetime desc
The format is not in php format, but you can see the only place you need a parameter is where the user ID is. All the details come along in the results including the respective avatars, titles, messages, from user and recipient user too. Take what you need in one query.
I would expect two individual indexes on your chatmsgs table. One on the sender, one on the receiver.