从MySQL数据库中查找下一个/上一个电视节目

Question

I've become rather stuck with a situation I have. I have a database with fields id, showid, season, episode and some other arbitrary data. I have a php page to display information about episodes of shows which works by having the id as a get variable. What I wish to achieve is to have a link to the next episode and previous episode of this tv program however the shows aren't necessarily in order and so simply incrementing or decrementing the id will not help. So I would fetch the episodes and store then in $rows with the following MySQL query:

SELECT id FROM episodes WHERE showid = $id ORDER BY season, episode;

Now without having to loop through the array (which could be rather large for some shows) is there an easy way for me to find the next and previous episode? I'm sure there is I just can't think of it.

Edit: I have been thinking about this myself and nothing all that helpful has come through yet (although thanks for the help, its much appreciated). What I have thought of is to make a query to see if a higher episode exists of the same season, if not make another query to find the lowest episode of then next lowest season - or something along those lines - and then repeat for previous. What do you think?

Edit 2: I thought I would post my final code for future reference. Here I find the id's of the nex and previous shows (if they exist).

Find the next episode:

try {
    // First check for a show of the same season but the next lowest episode number
    $stmt = $dbh->prepare("SELECT id FROM episodes WHERE showid = :show AND season = :s AND episode > :e ORDER BY episode LIMIT 1;");
    $stmt->execute($pars);
    $rows = $stmt->fetchAll();
    if(count($rows) > 0) { // If there is one this is our next id
        $nextid = $rows[0]['id'];
    } else {
        // Otherwise check for an episode of a higher season number
        $stmt = $dbh->prepare("SELECT id FROM episodes WHERE showid = :show AND season > :s ORDER BY season, episode LIMIT 1;");
        $stmt->execute($pars);
        $rows = $stmt->fetchAll();
        if(count($rows) > 0) { // If there is one this is our next id.
            $nextid = $rows[0]['id'];
        } // Otherwise no next id is set and so no next link will be created.
    }
} catch(PDOException $e) {
    die("Error: " . $e->getMessage());
}

Find the previous episode:

try {
    // First check for an episode in same season of the next highest episode number.
    $stmt = $dbh->prepare("SELECT id FROM episodes WHERE showid = :show AND season = :s AND episode < :e ORDER BY episode DESC LIMIT 1;");
    $stmt->execute($pars);
    $rows = $stmt->fetchAll();
    if(count($rows) > 0) { // If one is found then this is our prev id.
        $previd = $rows[0]['id'];
    } else {
        // Otherwise check for an episode of a lower season number.
        $stmt = $dbh->prepare("SELECT id FROM episodes WHERE showid = :show AND season < :s ORDER BY season DESC, episode DESC LIMIT 1;");
        $stmt->execute($pars);
        $rows = $stmt->fetchAll();
        if(count($rows) > 0) { // If there is one this is our prev id.
            $previd = $rows[0]['id'];
        } // Otherwise no prev id is set and so no prev link will be created.
    }
} catch(PDOException $e) {
    die("Error: " . $e->getMessage());
}

Then I have the following links:

if($previd) echo "<a href=\"/tv/view/" . $previd . "/\">Previous Episode</a>";
if($nextid) echo "<a href=\"/tv/view/" . $nextid . "/\">Next Episode</a>";

Answer 1

Why not doing it like a paginator of a table, but showing only one entry your actual page. You can do this by expading your query like this:

SELECT id FROM episodes WHERE showid = $id ORDER BY season, episode LIMIT 0,1;

Where the 0 is the offset. That means the starting record, which you have to increment. Here as an example:

SELECT id FROM episodes WHERE showid = $id ORDER BY season, episode LIMIT $page,1;

Then you only have to pass the page of the actual shown episode as GET parameter "?page=0" in you URL. Previous episode is page - 1 and next is page + 1.

Only pitfall is that you have to check for fist and las episode. To know when previous or next is not possible.

Answer 2

If the ids aren't in any particular order, then you'll have to basically scan the table for where you currently are, and then use the last fetched and about-to-fetch records as your prev/next episodes, eg

$row = mysql_fetch_assoc($result);
$previous_episode = $row['id']; // prime the system
do {
   if ($row['id'] == $id_of_current_episode) {
       $next_row = mysql_fetch_assoc($result);
       $next_episode = $row['id'];
       break;
   }
} while($row = mysql_fetch_assoc($result));

This won't handle the case where you're already at the last episode gracefully, but should get you started.

Answer 3

I posted 3 times in this thread my bad, but if your episodes and IDs aren't ordered then there's no way to do this as far as I know

Fix your IDs