EXPLAIN ANALYZE 
select
	supp_nation,
		cust_nation,
			l_year,
				sum(volume) as revenue
				from
					(
								select
											n1.n_name as supp_nation,
														n2.n_name as cust_nation,
																	extract(year from l_shipdate) as l_year,
																				l_extendedprice * (1 - l_discount) as volume
																						from
																									supplier,
																												lineitem,
																															orders,
																																		customer,
																																					nation n1,
																																								nation n2
																																										where
																																													s_suppkey = l_suppkey
																																																and o_orderkey = l_orderkey
																																																			and c_custkey = o_custkey
																																																						and s_nationkey = n1.n_nationkey
																																																									and c_nationkey = n2.n_nationkey
																																																												and (
																																																																	(n1.n_name = 'VIETNAM' and n2.n_name = 'CHINA')
																																																																					or (n1.n_name = 'CHINA' and n2.n_name = 'VIETNAM')
																																																																								)
																																																																											and l_shipdate between date '1995-01-01' and date '1996-12-31'
																																																																												) as shipping
																																																																												group by
																																																																													supp_nation,
																																																																														cust_nation,
																																																																															l_year
																																																																															order by
																																																																																supp_nation,
																																																																																	cust_nation,
																																																																																		l_year