QUERYPLAN---NestedLoopSemiJoin(cost=0.00..51.84rows=7width=28)->SeqScanonemployeese(cost=0.00..27.00rows=7width=28)Filter:(dept_id=3)->SeqScanondepartments(cost=0.00..24.50rows=1450width=0)(4rows)emp_id|emp_name---+---4|David5|Eve(2rows) 返回的是左表employees中dept_id为3的所有员...
explain select * from a left join ( b join c on b.y=c.bc) d on a.x=d.z; 执行计划如下 QUERY PLAN --- Nested Loop Left Join (cost=0.15..117392.81 rows=582 width=24) -> Seq Scan on a (cost=0.00..1.51 rows=51 width=8) -> Nested Loop (cost=0.15..2278.96 rows=2283 width...
-> Parallel Seq Scan on lineitem (cost=0.00..1312000.57 rows=14708428 width=5) (actual time=1.491..29217.070 rows=11767943 loop s=5) Nested loop joins · Parallel Index Only Scan tpch=# explain (costs off) select c_custkey, count(o_orderkey) from customer left outer join orders on c_...
内容1 : Nested Loop Join连接方式 内容2 : Merge Join连接方式 内容3 : Hash Join连接方式 多表连接方式 多表连接方式 三种连接方式: nested loop join merge join hash join 支持所有join操作: NATURAL INNER JOIN INNER JOIN LEFT/RIGHT OUTER JOIN FULL OUTER JOIN 嵌套循环连接方式 Nested Loop Join 嵌套...
gather发生在最后阶段,因此“Nested Loop Left Join”是并行操作。从版本10开始提供“Parallel Index Only Scan”。其行为与并行顺序扫描类似。条件c_custkey = o_custkey为每个客户行读取一个订单。 因此,它不是并行的。 哈希连接(Hash Join) 在PostgreSQL 11之前,每个worker都构建自己的哈希表。因此,4个以上的wo...
(cost=21.03..21.04rows=1width=128)Sort Key:c.relname −>Nested Loop LeftJoin(cost=0.00..21.02rows=1width=128)Join Filter:(n.oid=c.relnamespace)−>Seq Scan on pg_classc(cost=0.00..19.93rows=1width=72)Filter:((relkind=ANY('{r,p}'::"char"[]))AND(pg_g...−>Seq Scan on...
LEFT OUTER JOIN kc_itemfilter_lane AS kifl ON kifd.lane_di = kifl.di INNER JOIN _item AS ai ON ai.di = kifd.detail_di AND ai.delflg = 0 AND ai.is_enable = TRUE AND ai.is_package = FALSE AND ai.create__di = '160539' ...
-> Nested Loop Left Join -> Parallel Index Only Scan using customer_pkey on customer -> Index Scan using idx_orders_custkey on orders Index Cond: (o_custkey = customer.c_custkey) Filter: ((o_comment)::text !~~ '%special%deposits%'::text) ...
(1)连接操作的执行过程 ① 嵌套循环法(NESTED-LOOP) ② 排序合并法(SORT-MERGE) ③ 索引连接(INDEX-JOIN) (2)等值与非等值连接查询 (3)自身连接 (4)连接JOIN ① INNER JOIN (JOIN) ② LEFT JOIN (LEFT OUTER JOIN) ③ RIGHT JOIN (RIGHT OUTER JOIN) ④ FULL JOIN (FULL OUTER JOIN) ...
-> Nested Loop Left Join -> Parallel Index Only Scan using customer_pkey on customer -> Index Scan using idx_orders_custkey on orders Index Cond: (o_custkey = customer.c_custkey) Filter: ((o_comment)::text !~~ '%special%deposits%'::text) ...