public function set_query() {

		global $wpdb;

		$txn_meta_join  = '';
		$txn_meta_where = '';
		// create an "IN" clause that can be used for later in WHERE clauses.
		if ( $this->get_posted_students() || $this->get_posted_posts() ) {

			// get an array of order based on posted students & products.
			$this->set_order_data_query(
				array(
					'date_range'     => false,
					'query_function' => 'get_col',
					'select'         => array(
						'orders.ID',
					),
					'statuses'       => array(
						'llms-active',
						'llms-completed',
						'llms-refunded',
					),
				)
			);
			$this->query();
			$order_ids = $this->get_results();

			if ( $order_ids ) {

				$txn_meta_join   = "JOIN {$wpdb->postmeta} AS txn_meta ON txn_meta.post_id = txns.ID";
				$txn_meta_where .= " AND txn_meta.meta_key = '_llms_order_id'";
				$txn_meta_where .= ' AND txn_meta.meta_value IN ( ' . implode( ', ', $order_ids ) . ' )';
			} else {

				$this->query_function = 'get_var';
				$this->query          = 'SELECT 0';
				return;

			}
		}

		// date range will be used to get transactions between given dates.
		$dates            = $this->get_posted_dates();
		$this->query_vars = array(
			$this->format_date( $dates['start'], 'start' ),
			$this->format_date( $dates['end'], 'end' ),
		);

		$this->query_function = 'get_results';
		$this->output_type    = OBJECT;

		$this->query = "SELECT
							  txns.post_modified AS date
							, refund.meta_value AS amount
						FROM {$wpdb->posts} AS txns
						{$txn_meta_join}
						JOIN {$wpdb->postmeta} AS refund ON refund.post_id = txns.ID
						WHERE
						        ( txns.post_status = 'llms-txn-succeeded' OR txns.post_status = 'llms-txn-refunded' )
						    AND txns.post_type = 'llms_transaction'
							AND txns.post_date BETWEEN CAST( %s AS DATETIME ) AND CAST( %s AS DATETIME )
							AND refund.meta_key = '_llms_refund_amount'
							{$txn_meta_where}
							ORDER BY txns.post_modified ASC
						;";

	}