PHP - Unir resultados sql a un array

<?php

include ("conexion.php") ;

//$sql="SELECT group_concat(tags) FROM tag";

$sql ="SELECT tags FROM tag";

$result=mysql_query($sql)or die (mysql_error ());

while ($fila=mysql_fetch_array($result)) {

$bb=$fila[0];

$bb=explode(", ",$fila[0]); //creo un array por cada columna  Array ( [0] => naturaleza [1] => paisaje [2] => ) ...etc

//$bb=array_unique($bb); 

foreach($bb as $tags){ //separo individualmente cada palabra

echo "<br>";

echo "<a href='y.php?id_post=$tags'>$tags</a>";

  }

} //salgo del bucle while

?>

<?php

include ("conexion.php") ;

$sql ="SELECT tags FROM tag";

$result=mysql_query($sql)or die (mysql_error ());

$tags = array();

while ($fila=mysql_fetch_array($result)) {

    $tags_post = explode(", ",$fila[0]);

    foreach ($tags_post as $tag_post) {

        if ( ! in_array($tag_post, $tags)) {

            array_push($tags, $tag_post);

        }

    }

}

foreach ($tags as $tag) {

    echo "<br>";

    echo "<a href='y.php?id_post=$tag'>$tag</a>";

}

<?php

include ("conexion.php") ;

$sql ="SELECT tags FROM tag";

$result=mysql_query($sql)or die (mysql_error ());

$tags = array();

while ($fila=mysql_fetch_array($result)) {

    $tags += explode(", ",$fila[0]);

}

$tags = array_unique($tags);

foreach ($tags as $tag) {

    echo "<br>";

    echo "<a href='y.php?id_post=$tags'>$tags</a>";

}