php - Is it possible to use placeholders on <input type="submit">?

Solution:

No, but buttons can have different values and labels.

<button name="foo" value="bar">baz</button>

Solution:

Since you are using a form-tag per row, you can add a hidden input-field in the form and set the value of the submit-button to whatever you like.

<form method="post" action="Details.php">
   <input type="hidden" name="id" value="<?php echo $data[$i1]; ?>" />
   <input type="submit" name="Overview" value="test" />
</form>