Mysql build query with multiple constraints - php

Question

I am trying to set up a query that outputs the 5 most read articles over the last 4hrs. However, if there are no new articles over the last 4hrs, the list will be empty. What I would like is a query that outputs 5 articles over the last 4hrs. If there are no 5 articles in the last 4hrs, but lets say only 2, I would like to add 3 more newest articles to the list (sorted by log_time).
So the query should always output 5 articles.
I am wondering if this can be done in one query.
$sqlCommand = "SELECT * FROM feeds where category like '$category' AND log_time > NOW() - INTERVAL 4 HOUR ORDER BY feed_hits DESC LIMIT 5";
$query = mysqli_query($myConnection, $sqlCommand) or die (mysqli_error());
While ($row = mysqli_fetch_array($query)) {
$fid1 = $row["id"];
$feed_id1 = $row["feed_id"];
$link1 = $row["link"];
$title1 = $row["title"];
$output .= '' . $title1 . '<br/>';
}
mysqli_free_result($query);
echo $output;

Answer 1

You can achieve this via a UNION query. The first half of the below query is simply your original query, which may return up to 5 matching records. The second half of the query returns an arbitrary number of records which are older than 4 hours. The entire query is then ordered by log time, with a limit of 5. This puts your recent target records first, with the older records taking any available positions should they be needed.
SELECT *
FROM
(SELECT * FROM feeds
WHERE category like '$category' AND log_time > NOW() - INTERVAL 4 HOUR
ORDER BY feed_hits DESC LIMIT 5) t1
UNION ALL
(SELECT * FROM feeds
WHERE category like '$category' AND log_time <= NOW() - INTERVAL 4 HOUR) t2
ORDER BY log_time DESC
LIMIT 5;

Answer 2

You could not limit for 4 HOUR and order by log_time limit 5
"SELECT *
FROM feeds
where category like '$category'
ORDER BY log_time DESC LIMIT 5";
and if you need ordered by feed_hits you can reorder the result set
"select * from ( SELECT *
FROM feeds
where category like '$category'
ORDER BY log_time DESC LIMIT 5 ) t order by feed_hits ";

Answer 3

Simply remove the time filtering and instead order by time, this will always give you the latest:
SELECT * FROM feeds WHERE category LIKE '$category' ORDER BY log_time DESC, feed_hits DESC LIMIT 5