Pulling latest post from table - php

Question

All,
I am trying to display the latest post from my authors.
The posts are in one table, the author in another. The queries used were: join on a column called content_id, and I am trying to work with MAX(item_date) which is the date the post was published.
Here are some queries I am running and the output, I seem to be getting everything except the latest posts from all authors:
First (and this bit is working) we need to get information about the author:
$query="SELECT content_id, title, source_image, url FROM content_detail where approved='y'";
$result1 = $mysqli->query($query) or die($mysqli->error.__LINE__);
// GOING THROUGH THE DATA
if($result1->num_rows > 0) {
while($fetch=mysqli_fetch_array($result1)) {
$title=$fetch['title'];
$feed_rss=$fetch['url'];
$content_id=$fetch['content_id'];
$source_image=$fetch['source_image'];
Now on that basis lets get the posts, round 1:
$query2 = "SELECT item_id, item_title, MAX(item_date) as item_date from posts WHERE content_id='$content_id' GROUP BY content_id";
$result2 = $mysqli->query($query2) or die($mysqli->error.__LINE__);
if($result2->num_rows > 0) {
while($rows2=mysqli_fetch_array($result2)) {
$item_id = $rows2['item_id'];
$item_title = $rows2['item_title'];
$item_date = $rows2['item_date']; `
This pulls back an in interesting set of results, the latest date of a post from an author, but not the latest title!
I have tried GROUP BY item_title and content_id to no avail.
The following pulls back just records that have more than one date in the database, the problem is (as this is new) some authors only have one post, these are not being displayed:
$query2 = "SELECT item_id, item_title, item_date FROM posts AS a WHERE content_id = content_id AND item_date = (
SELECT MAX(item_date)
FROM rssingest AS b
)
";
I have tried:
ORDER BY DATE DESC LIMIT 1
at the end of my queries to no avail.
item_date is a DATE type in the table.
Any help would be greatly appreciated!
Thanks,

Answer 1

You are running this query to get the maximum date:
SELECT item_id, item_title, MAX(item_date) as item_date
from posts
WHERE content_id = '$content_id'
GROUP BY content_id;
Of course you don't get the right item_title. It is not mentioned in the group by clause and has no aggregation function. So, you are using a MySQL extension (this query would fail in other databases).
You can get the most recent title using the substring_index()/group_concat() trick:
SELECT max(item_id),
substring_index(group_concat(item_title separator '|' order by item_date desc), '|', 1) as last_title,
MAX(item_date) as item_date
from posts
WHERE content_id = '$content_id'
GROUP BY content_id;
This will return one row. But, if there is only one row that you want, you can do:
SELECT p.*
from posts p
WHERE p.content_id = '$content_id'
ORDER BY item_date desc
LIMIT 1;
The previous version will generalize if you add a group by statement.

Answer 2

You need to join your posts table with itself to grab only the newest post for each content_id (which I believe is the author).
$query2 = "SELECT posts.item_id, posts.item_title, posts.item_date from posts
join (select max(item_id) max_id, content_id from posts group by content_id) maxid
on maxid.content_id=posts.content_id and maxid.max_id=posts.item_id
WHERE content_id='$content_id' ";
This opens the door for further optimization. You could grab the authors and their last post in one run.
SELECT content_detail.content_id,
content_detail.title,
content_detail.source_image,
content_detail.url ,
posts.item_id,
posts.item_title,
posts.item_date
FROM content_detail
join posts on content_detail.content_id=posts.content_id
join (select max(item_id) max_id, content_id from posts group by content_id) maxid
on maxid.content_id=posts.content_id and maxid.max_id=posts.item_id
where content_detail.approved='y'
But this could be an overstatement. You should of course try it yourself :)