请假各位大哥 pg 中一个相对比较简单的查询为什么效率这么低

其实就是一个主表，里面有两个指向明细表的索引。

create table pairs1(id serial primary key, ai int not null, bi int not nul); create table pairs2(id serial primary key, ai int not null, bi int not null); create table items1(id serial primary key, name text not null); create table items2(id serial primary key, name text not null); create view pairs as select * from pairs1 union all select * from pairs2; create view items as select * from items1 union all select * from items2; create view viewpairs as select t0.id, t1.id as aid, t1.name as aname, t2.id as bid, t2.name as bname from pairs t0 left join items t1 on t0.ai=t1.id left join items t2 on t0.bi=t2.id; 

$ explain select * from viewpairs; QUERY PLAN ------------------------------------------------------------------------------------------------------- Merge Right Join (cost=5319.09..15347.88 rows=658063 width=76) Merge Cond: (items1_1.id = pairs1.bi) -> Merge Append (cost=0.32..151.82 rows=2540 width=36) Sort Key: items1_1.id -> Index Scan using items1_pkey on items1 items1_1 (cost=0.15..63.20 rows=1270 width=36) -> Index Scan using items2_pkey on items2 items2_1 (cost=0.15..63.20 rows=1270 width=36) -> Sort (cost=5318.77..5448.31 rows=51816 width=44) Sort Key: pairs1.bi -> Merge Right Join (cost=326.20..1261.29 rows=51816 width=44) Merge Cond: (items1.id = pairs1.ai) -> Merge Append (cost=0.32..151.82 rows=2540 width=36) Sort Key: items1.id -> Index Scan using items1_pkey on items1 (cost=0.15..63.20 rows=1270 width=36) -> Index Scan using items2_pkey on items2 (cost=0.15..63.20 rows=1270 width=36) -> Sort (cost=325.88..336.08 rows=4080 width=12) Sort Key: pairs1.ai -> Append (cost=0.00..81.20 rows=4080 width=12) -> Seq Scan on pairs1 (cost=0.00..30.40 rows=2040 width=12) -> Seq Scan on pairs2 (cost=0.00..30.40 rows=2040 width=12) (19 rows) 

问了 ai ，提示在 pairs1 和 pairs2 中为 ai 和 bi 创建索引，但我总觉得有点不靠谱。