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function count_page_hits() {
   if ( is_single() ) {
      global $post;
      $count = get_post_meta( $post -> ID, 'count_page_hits', true );
      $newcount = $count + 1;
 
      update_post_meta( $post -> ID, 'count_page_hits', $newcount );
   }
}
add_action( 'wp_head', 'count_page_hits' );

***
MORE USABLE
// function to display number of posts.
function getPostViews($postID){
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
        return "0 View";
    }
    return $count.' Views';
}

// function to count views.
function setPostViews($postID) {
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        $count = 0;
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
    }else{
        $count++;
        update_post_meta($postID, $count_key, $count);
    }
}

on single.php/page.php --> setPostViews( get_the_ID() );
for echo --> echo getPostViews(get_the_ID());

Simple echo on backend -->
add_filter('manage_posts_columns', 'posts_column_views');
add_action('manage_posts_custom_column', 'posts_custom_column_views',5,2);
function posts_column_views($defaults){
    $defaults['post_views'] = __('Views');
    return $defaults;
}
function posts_custom_column_views($column_name, $id){
	if($column_name === 'post_views'){
        echo getPostViews(get_the_ID());
    }
}