性能优化技巧：预关联

select       l_year,       sum(volume) as revenuefrom       (              select                     extract(year from l_shipdate) as l_year,                     (l_extendedprice * (1 - l_discount) ) as volume              from                     orderdetail,                     part              where                     p_partkey = l_partkey                     and length(p_type)>2       ) shippinggroup by       l_yearorder by       l_year;

select       l_year,       sum(volume) as revenuefrom       (              select                     extract(year from l_shipdate) as l_year,                     (l_extendedprice * (1 - l_discount) ) as volume              from                     supplier,                     orderdetail,                     orders,                     customer,                     part,                     nation n1,                     nation n2              where                     s_suppkey = l_suppkey                     and p_partkey = l_partkey                     and o_orderkey = l_orderkey                     and c_custkey = o_custkey                     and s_nationkey = n1.n_nationkey                     and c_nationkey = n2.n_nationkey                     and length(p_type) > 2                     and n1.n_name is not null                     and n2.n_name is not null                     and s_suppkey > 0       ) shippinggroup by       l_yearorder by       l_year;