Check table to see if array items already exist

Hi all,

I have been confusing myself for days over this so bear with me if it gets a bit confusing.

I have a table called tags with columns id, name which list all unique tags (linux, php, mysql, etc.). And I have an array that includes some tags that have been entered:

$tags = array('linux,php,mysql');

Now when the array has just one tag I can search the tags table and return whether the tag already exists in the table or not. But I am unsure how I can go about checking for each array item. My thinking on how to go about this (and I could be wrong) is:

1. Explode the array.
2. Check the first item in the array to the table.
3. If it does not exist, put it into a separate array.
4. Once all items have been iterated, store these unique tags in the table.

For reference, currently I have:

function tagExists($pdo, $tag) {
  $stmtTagExists = $pdo->prepare('SELECT * FROM tags WHERE name=?');
  $stmtTagExists->execute([$tag]);
  return $stmtTagExists->fetch(PDO::FETCH_ASSOC);
}

$tags = array('linux');

foreach($tags as $item) {
        if (tagExists($pdo, $item)) {
          echo 'The tag ' . $item . ' exists! <br>';
        } else {
          echo 'The tag ' . $item . ' does not exist! <br>';
        }
      }

If you need any clarification on anything, just ask.

TIA