Source

File: wp-includes/wp-db.php

public function flush() {
		$this->last_result   = array();
		$this->col_info      = null;
		$this->last_query    = null;
		$this->rows_affected = 0;
		$this->num_rows      = 0;
		$this->last_error    = '';

		if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
			mysqli_free_result( $this->result );
			$this->result = null;

			// Sanity check before using the handle.
			if ( empty( $this->dbh ) || ! ( $this->dbh instanceof mysqli ) ) {
				return;
			}

			// Clear out any results from a multi-query.
			while ( mysqli_more_results( $this->dbh ) ) {
				mysqli_next_result( $this->dbh );
			}
		} elseif ( is_resource( $this->result ) ) {
			mysql_free_result( $this->result );
		}
	}