Source

File: wp-includes/comment.php

function get_comment_count( $post_id = 0 ) {
	global $wpdb;

	$post_id = (int) $post_id;

	$where = '';
	if ( $post_id > 0 ) {
		$where = $wpdb->prepare( 'WHERE comment_post_ID = %d', $post_id );
	}

	$totals = (array) $wpdb->get_results(
		"
		SELECT comment_approved, COUNT( * ) AS total
		FROM {$wpdb->comments}
		{$where}
		GROUP BY comment_approved
	",
		ARRAY_A
	);

	$comment_count = array(
		'approved'            => 0,
		'awaiting_moderation' => 0,
		'spam'                => 0,
		'trash'               => 0,
		'post-trashed'        => 0,
		'total_comments'      => 0,
		'all'                 => 0,
	);

	foreach ( $totals as $row ) {
		switch ( $row['comment_approved'] ) {
			case 'trash':
				$comment_count['trash'] = $row['total'];
				break;
			case 'post-trashed':
				$comment_count['post-trashed'] = $row['total'];
				break;
			case 'spam':
				$comment_count['spam']            = $row['total'];
				$comment_count['total_comments'] += $row['total'];
				break;
			case '1':
				$comment_count['approved']        = $row['total'];
				$comment_count['total_comments'] += $row['total'];
				$comment_count['all']            += $row['total'];
				break;
			case '0':
				$comment_count['awaiting_moderation'] = $row['total'];
				$comment_count['total_comments']     += $row['total'];
				$comment_count['all']                += $row['total'];
				break;
			default:
				break;
		}
	}

	return array_map( 'intval', $comment_count );
}