Catgories didn't work - php

Question

So I try to learn php and decided to make one site where I add images, save them in folder and id, name,type, path in mysql. Then show on page. So far I have upload form and I can upload and save images. Also I showing them successfully on the page.
Now I'm trying to make categories like - Nature, Funny ... etc. So I added one field in my main table -> img_category.
Also I madded second table - cats whit cat_id and cat_name fields. Using this to show the categories on the page:
<?php
$q = mysqli_query($con,"select * from cats");
while ($res = mysqli_fetch_assoc($q))
{
echo '<a href="pic.php?cat_id='. $res['cat_id'] .'">'.$res['cat_name'].'<br/>';
}
So now how can I make when I click on some category link to load images only from this category?
I have managed to make something like this but it doesn't work like is expected
<?php
$q = mysqli_query($con,"select * from cats");
while ($res = mysqli_fetch_assoc($q))
{
echo '<a href="pic.php?cat_id='. $res['cat_id'] .'">'.$res['cat_name'].'<br/>';
}
?>
<hr>
<?php
$cat_id = $_GET['cat_id'];
$query = "SELECT * FROM images JOIN cats ON images.img_category = cats.cat_id WHERE cats.cat_id = '$cat_id'";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
$line = mysqli_fetch_array($result, MYSQL_BOTH);
if (!$line) echo '';
$previd = -1;
$currid = $line[0];
if (isset($_GET['id'])) {
do {
$currid = $line[0];
if ($currid == $_GET['id']) break;
$previd = $currid;
$line = mysqli_fetch_array($result, MYSQL_BOTH);
} while ($line);
}
if ($line) {
echo "<div id=\"picture\">";
echo "<img style=\"width:100%;margin:0 auto;\" src=\"upload/".$line['name']."\" /></a><br />";
echo "<div id=\"caption\">".$line['caption']."</div><br />";
}
else echo "There is no images!\n";
if ($previd > -1) echo '<span>Prev</span>';
echo str_repeat(' ', 5);
$line = mysqli_fetch_array($result, MYSQL_BOTH);
$query = "select * from images order by RAND() LIMIT 1";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
while ($row = mysqli_fetch_array($result, MYSQL_BOTH)){
echo 'Random';
}
echo str_repeat(' ', 5);
if ($line) echo '<span>Next</span> <br /><br />';
echo "</div>";
?>
The results are:
When there is image in the category is showed but and if I click on 'Next' button I get the same image.
If there is no image in the category I get all echoes like link whit the ID of last category for exam: There is no image like link and if I click it I get last category ID loaded. In my case I have 8 categories so ID=8.
Any help is appreciate!
Thank's
EDIT:
Ok this line:
echo '<span>Следваща</span>
Where is pic.php?cat_id=... i think is wrong. Here I must take next image ID not next category ID. But how to change it for image? If i make it pic.php?id=... I get empty page.
I don't understand it. I know that is messy code but is best I can do for now.
EDIT 2:
I've made something like this. Now can you help me how to make query's for next image because now didn't get next image and stay the same.
$cat_id = $_GET['cat_id'];
$cat_id = mysqli_real_escape_string($con, $cat_id);
$query = "SELECT * FROM images JOIN cats ON images.img_category = cats.cat_id WHERE cats.cat_id = '$cat_id'";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
$prevSQL = mysqli_query($con,"SELECT cat_id FROM cats WHERE cat_id < $cat_id ORDER BY cat_id DESC LIMIT 1") or die (mysqli_error($con));
$nextSQL = mysqli_query($con, "SELECT cat_id FROM cats WHERE cat_id > $cat_id ORDER BY cat_id ASC LIMIT 1") or die (mysqli_error($con));
$prevobj=mysqli_fetch_object($prevSQL);
$nextobj=mysqli_fetch_object($nextSQL);
$pc = mysqli_fetch_object(mysqli_query($con, "SELECT COUNT(cat_id) as pid FROM cats WHERE cat_id<$cat_id ORDER BY cat_id DESC")) or die (mysqli_error($con));
$nc = mysqli_fetch_object(mysqli_query($con, "SELECT COUNT(cat_id) as nid FROM cats WHERE cat_id>$cat_id ORDER BY cat_id ASC")) or die (mysqli_error($con));
$prev=$pc->pid>0 ? 'Prev |' : '';
$next=$nc->nid>0 ? 'Next' : '';
$row = mysqli_fetch_array($result);
echo "<div id=\"picture\">";
echo "<img src=\"upload/" . $row['name'] . "\" alt=\"\" /><br />";
echo $row['caption'] . "<br />";
echo "</p>";
echo $prev;
echo $next;

Answer 1

As you stated, I guess the error is with the line:
echo '<span>Следваща</span>
I think it should be:
echo '<span>Следваща</span>
EDIT:
Your code should look like:
<?php
$q = mysqli_query($con,"select * from cats");
while ($res = mysqli_fetch_assoc($q))
{
echo '<a href="pic.php?cat_id='. $res['cat_id'] .'">'.$res['cat_name'].'<br/>';
}
?>
<hr>
<?php
$cat_id = $_GET['cat_id'];
$query = "SELECT * FROM images JOIN cats ON images.img_category = cats.cat_id WHERE cats.cat_id = '$cat_id'";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
$line = mysqli_fetch_array($result, MYSQL_BOTH);
if (!$line) echo '';
$previd = -1;
$currid = $line[0];
if (isset($_GET['id'])) {
do {
$currid = $line[0];
if ($currid == $_GET['id']) break;
$previd = $currid;
$line = mysqli_fetch_array($result, MYSQL_BOTH);
} while ($line);
}
if ($line) {
echo "<div id=\"picture\">";
echo "<img style=\"width:100%;margin:0 auto;\" src=\"upload/".$line['name']."\" /></a><br />";
echo "<div id=\"caption\">".$line['caption']."</div><br />";
}
else echo "There is no images!\n";
if ($previd > -1) echo '<span>Prev</span>';
echo str_repeat(' ', 5);
$line = mysqli_fetch_array($result, MYSQL_BOTH);
$query = "select * from images order by RAND() LIMIT 1";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
while ($row = mysqli_fetch_array($result, MYSQL_BOTH)){
echo 'Random';
}
echo str_repeat(' ', 5);
if ($line) echo '<span>Next</span> <br /><br />';
echo "</div>";
?>

Answer 2

Try this
<?php
if(isset($_GET['cat_id'])){
$cat_id = $_GET['cat_id'];
$query = "SELECT * FROM images WHERE img_category = '$cat_id'";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
$line = mysqli_fetch_array($result, MYSQL_BOTH);
if (!$line) echo '';
$previd = -1;
$currid = $line[0];
if (isset($_GET['id'])) {
$previous_ids = array();
do {
$previous_ids[] = $line[0];
$currid = $line[0];
if ($currid == $_GET['id']) break;
$previd = end($previous_ids);
$line = mysqli_fetch_array($result, MYSQL_BOTH);
} while ($line);
}
if ($line) {
echo "<div id=\"picture\">";
echo "<img style=\"width:100%;margin:0 auto;\" src=\"upload/".$line['name']."\" /><br />\r";
echo "<div id=\"caption\">".$line['caption']."</div><br />";
}
else echo "There is no images!\n";
if ($previd > -1)
echo '<span>Prev</span>';
echo str_repeat(' ', 5);
$line = mysqli_fetch_array($result, MYSQL_BOTH);
$query = "select * from images WHERE img_category = '$cat_id' order by RAND() LIMIT 1";
$result = mysqli_query($con, $query) or die("Query failed: " . mysqli_errno($con));
while ($row = mysqli_fetch_array($result, MYSQL_BOTH)){
echo 'Random';
}
echo str_repeat(' ', 5);
if ($line) echo '<span>Next</span> <br /><br />';
echo "</div>\r";
}
?>