Creating Next and Previous buttons for navigation using mysql result

Question

I have taken the working code from this thread: Creating Next and Previous buttons for navigation

It works for me but right now I would like to ask is there any way to disable the link if it reaches the 1st or the last ID?

Here's my brief code:

function getNavID($id) {

$result4= mysql_query("SELECT 
( SELECT id FROM products_list WHERE id > '$id' LIMIT 1 )
AS nextValue,
( SELECT id FROM products_list WHERE id < '$id' ORDER BY id DESC LIMIT 1 )
AS prevValue
FROM products_list");
if ($resultID = mysql_fetch_array($result4)) {
    return $resultID;
}
else {
    return NULL;
}
}

$LinkID = getNavID($id);

<p><a href="update.php?id=<?php echo urlencode($LinkID['prevValue']); ?>">Previous</a></p>
<p><a href="update.php?id=<?php echo urlencode($LinkID['nextValue']); ?>">Next</a></p>

Let's say the page I'm on now is ID=1 so logically, there is no ID lesser than 1. Is there any way that I can do to disable the links if the ID reaches the min and max ID ?

Thanks in advance guys.

Regards, Jeff

Community · Accepted Answer · 2017-05-23 11:58:23Z

2

For ID=1, $LinkID['prevValue'] should return NULL, which you can check easily. Include a check, so that you only print the link if there is a previous/next value, e.g.:

<p>
<?php
    if (!is_null($LinkID['prevValue'])) {
>?
    <a href="update.php?id=<?php echo urlencode($LinkID['prevValue']); ?>">Previous</a>
<?php
    } else {
        echo "No previous entries.";
    }
?>
</p>

And analogously for Next entry.

By the way, just for completeness' sake, I would rewrite the SQL statement like this:

SELECT 
    ( SELECT id FROM products_list
        WHERE id > '$id' LIMIT 1 ) AS nextValue,
    ( SELECT id FROM products_list
        WHERE id < '$id' ORDER BY id DESC LIMIT 1 ) AS prevValue
    FROM products_list
    LIMIT 1

I.e. an additional LIMIT 1 at the end. You might not notice a difference in your result, but with your statement, the database delivers one row per entry in the table products_list (of which you only use the first, and they are all equal).

edited May 23, 2017 at 11:58

CommunityBot

11 silver badge

answered Aug 21, 2012 at 10:56

codeling

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2 Comments

Dr3am3rz Over a year ago

Hi, thanks for the reply. I've tried your code but it's not working. It show me a blank page.

codeling Over a year ago

I think I missed a parenthesis, I will correct that. In such cases (blank page), check the server log (or enable display of errors in browser (display_errors setting in php.ini, but enable that only if you're not on a production system!).

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