Adicionar campo checkout

functions.php

//Adicionar  campo no checkout e nova coluna no painel admin

/*Add the field to the checkout*/
add_action('woocommerce_before_order_notes', 'my_custom_checkout_field');

function my_custom_checkout_field( $checkout ) {

    echo '<div id="my_custom_checkout_field"><h3>'.__('Como nos conheceu?').'</h3>';

    woocommerce_form_field( 'my_field_name', array(
        'type'          => 'select',
        'class'         => array('my-field-class form-row-wide'),
	'required' 		=> true,
        'label'         => __('Escolha uma opção'),
        'placeholder'       => __('Enter something'),
	'options'     => array(
		'' => __(''),
        'pelo Google' => __('Pelo Google', 'woocommerce' ),
        'pelo Facebook' => __('Pelo Facebook', 'woocommerce' ),
		'pelo blog Site da Mamãe' => __('Pelo blog Site da Mamãe', 'woocommerce' ),
		'por indicação' => __('Por indicação', 'woocommerce' )
        )
        ), $checkout->get_value( 'my_field_name' ));

    echo '</div>';

}

/*Process the checkout*/
add_action('woocommerce_checkout_process', 'my_custom_checkout_field_process');

function my_custom_checkout_field_process() {
    global $woocommerce;

    // Check if set, if its not set add an error.
    if (!$_POST['my_field_name'])
         $woocommerce->add_error( __('Please enter something into this new shiny field.') );
}

/*Update the order meta with field value*/
add_action('woocommerce_checkout_update_order_meta', 'my_custom_checkout_field_update_order_meta');

function my_custom_checkout_field_update_order_meta( $order_id ) {
    if ($_POST['my_field_name']) update_post_meta( $order_id, 'Como nos conheceu?', esc_attr($_POST['my_field_name']));
}



//Define columns position and names

add_filter( 'manage_edit-shop_order_columns', 'MY_COLUMNS_FUNCTION' );
function MY_COLUMNS_FUNCTION($columns){
    $new_columns = (is_array($columns)) ? $columns : array();
    unset( $new_columns['order_actions'] );
    //edit this for you column(s)
    //all of your columns will be added before the actions column
    $new_columns['MY_COLUMN_ID_1'] = 'Como nos conheceu?';
    //stop editing
    $new_columns['order_actions'] = $columns['order_actions'];
    return $new_columns;
}

//Show values
add_action( 'manage_shop_order_posts_custom_column', 'MY_COLUMNS_VALUES_FUNCTION', 2 );
function MY_COLUMNS_VALUES_FUNCTION($column){
    global $woocommerce;
    $data = get_post_meta( $order_id );
	

$columns = array();
$columns["MY_COLUMN_ID_1"]    = __( 'my_field_name', 'woocommerce' );    

    //stop editing
}


//make the columns sortable
add_filter( "manage_edit-shop_order_sortable_columns", 'MY_COLUMNS_SORT_FUNCTION' );
function MY_COLUMNS_SORT_FUNCTION( $columns ) {
    $custom = array(
        //start editing

        'MY_COLUMN_ID_1'    => 'MY_COLUMN_1_POST_META_ID',
        //stop editing
    );
    return wp_parse_args( $custom, $columns );
}