Question

$db = new PDO("mysql:host=$hostname;dbname=$database", $username, $password);

            $items = 'SELECT items FROM menus';
            $itemLink = 'SELECT itemLink FROM menus';

            $itemQuery = $db->query($items);
            $linkQuery = $db->query($itemLink);

            $fetchItem = $itemQuery->fetch(PDO::FETCH_ASSOC);
            $fetchLink = $linkQuery->fetch(PDO::FETCH_ASSOC);

            $merged = array_merge($fetchItem,$fetchLink);

            foreach($merged as $key=>$value){
                echo "${key} =>  ${value} <br />";
            }

This is what it looks like in the database:

items   |itemLink
----------------------
Kill Bill|Kill Bill link
Preman  |Preman link

So, the expected output, or at least what I thought must be this:

    items => Kill Bill
    items => Preman
    itemLink => Kill Bill Link 
    itemLink => Preman Link

But the resulted output from the code is this:

items => Kill Bill
itemLink => Kill Bill Link 

It’s missing the other items and itemLink

So, how do I achieve the output that I want?

Answer 1

        $fetchItem = $itemQuery->fetch(PDO::FETCH_ASSOC);
        $fetchLink = $linkQuery->fetch(PDO::FETCH_ASSOC);

This only fetches the first row of each resultset. You need fetchAll:

        $fetchItem = $itemQuery->fetchAll(PDO::FETCH_ASSOC);
        $fetchLink = $linkQuery->fetchAll(PDO::FETCH_ASSOC);

and adjust the rest of your code.

        foreach($merged as $entry) {
          foreach( $entry as $key => $value ) {
            echo "${key} =>  ${value} <br />";
          }
        }

EDIT:
The call of fetch only retrieved the first row of the resultset, whereas fetchAll parses the complete resultset into an Array. So the Objects look like this afterwards:

Array(
  [0] => { 'items' => 'Kill Bill' },
  [1] => { 'items' => 'Preman' }
)
Array(
  [0] => { 'itemLink' => 'Kill Bill' },
  [1] => { 'itemLink' => 'Preman' }
)

array_merge concatenate both arrays to the following:

Array(
  [0] => { 'items' => 'Kill Bill' },
  [1] => { 'items' => 'Preman' },
  [2] => { 'itemLink' => 'Kill Bill' },
  [3] => { 'itemLink' => 'Preman' }
)

So we now have a two dimensional array. To traverse the values we need first to select each $entry, which is done in the outer foreach and can afterwards access the key/value structure in the inner foreach.

As pointed out in the other comment: If you want to preserve the connection between itemsand itemLink, you should change the query in the first place to

SELECT items, itemLink FROM menus