Read and Write into Wordpress MySQL

notes.php

This is a tutorial on how to 
** Insert form data on Database and
** Display Data from DB in Wordpress

<!-- *********************************  -->

<!-- Table Schema in MySQL -->
// 1. Here is the table schema we are using.
CREATE TABLE `books` (
  `id` int(11) NOT NULL,
  `title` varchar(100) NOT NULL,
  `author` varchar(100) NOT NULL
) ENGINE =InnoDB  DEFAULT CHARSET=utf8;

<!-- *********************************  -->

2. Create a template file in your theme directory and insert the following code 
----------- > copy code from another page to get the structure of a page in your theme.


Add the following on top of the page

/*
Template Name: Book Registration Form
*/

<!-- book_registration_template.php >>>>>> Registration Form Template -->
<form role="form" method="post">
  <div class="form-group">
      <input id="title" name="title" type="text" placeholder="Book Title" class="form-control input-sm" required="">  
  </div> 
  <div class="form-group">
      <input id="author" name="author" type="text" placeholder="Primary Author" class="form-control input-sm" required="">
  </div>      
  <div class="row justify-content-center">
      <div class="col-xs col-sm-4 col-md-4">
          <input type="submit" value="Submit" class="btn btn-info btn-block" name="submitbtn">
      </div>
  </div>  
</form>

<!---- ************************************************************* ---> 

3. Insert the following code in functions.php
<!--- Save to DB code in functions.php  -->
<?php
    if(isset($_POST['submitbtn'])) {
        $data = array(
            'title' => $_POST['title'],
            'author' => $_POST['author'],
            );
      $table_name = 'books';
      
      $result = $wpdb->insert($table_name, $data, $format=NULL);
      
      if ($result==1){
          echo "<script> alert('Book Saved');</script>";
      }else{
          echo "<script>alert('Unable to Save');</script>";
      }
    }      
        
?>
<!-- ********************************************************** -->
4. Create a page that uses this tempate

<!-- ********************************************************** -->

TO DISPLAY DB DATA 

5. Create another template in your theme directory and insert the following code. 
<!--  view_books_template.php >>> Display Data from DB -->

<?php
    global $wpdb;
    $result = $wpdb->get_results("select * from books");
?>
    <table class="table table-striped">
      <thead>
        <tr>
          <th>Book Title</th>
          <th>Primary Author</th>
        </tr>
      </thead>
      <tbody>
    <?php
        foreach ($result as $book) {?>
      <tr>
        <td><?php echo $book->title; ?> </td>
        <td><?php echo $book->author; ?> </td>
      </tr>      
         <?php } ?> 
      </tbody>
    </table>

6. Create a page that uses view_books_template.php template

Source code for the following video: https://www.youtube.com/watch?v=nj2DKyQn6Gs