WordPress — Query all posts in a taxonomy

functions.php

<?php
// Add a new public query variable: taxonomy_archive
add_filter ( 'query_vars', 'add_taxonomy_query_var' );

function add_taxonomy_query_var( $query_vars ) {
	$query_vars['taxonomy_archive'] = '';
	return $query_vars;
}

add_action( 'posts_clauses', 'taxonomy_archive_clauses', 10, 2 );

function taxonomy_archive_clauses( $pieces, $query ) {
	global $wpdb;

	$archive_query = $query->get( 'taxonomy_archive' );

	// Check if it's a query for a taxonomy archive
	if ( !empty( $archive_query ) ) {

		// Query for the taxonomy provided in the taxonomy_archive query variable
		$pieces['join'] .= " INNER JOIN {$wpdb->term_relationships} tr_tarchive ON ($wpdb->posts.ID = tr_tarchive.object_id)";
		$pieces['join'] .= " INNER JOIN {$wpdb->term_taxonomy} tt_tarchive ON (tr_tarchive.term_taxonomy_id = tt_tarchive.term_taxonomy_id)";
		$pieces['where'] .= $wpdb->prepare( " AND tt_tarchive.taxonomy = %s", $archive_query );
	}

	return $pieces;
}

template.php

<?php
// Query for all posts that have terms from the movie custom taxonomy
$args = array(
	'post_type' => array( 'post' ),
	'taxonomy_archive' => 'movie',
);

// the query
$the_query = new WP_Query( $args ); ?>

<?php if ( $the_query->have_posts() ) : ?>

	<!-- the loop -->
	<?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
		<!-- Loop stuff here -->
	<?php endwhile; ?>
	<!-- end of the loop -->

	<?php wp_reset_postdata(); ?>
<?php else : ?>
	<p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
<?php endif; ?>