我已经找了一个星期了，恐怕这个可能还不存在。我想在postgresql中使用一个跨多个表的索引。oracle和sqlserver似乎实现了它们（或多或少有一些选择）。
它对于我需要实现的一些搜索可能非常有用。
以下是针对oracle和sql server的多表索引示例，以供参考：
oracle示例
oracle可以创建位图连接索引，如下所示：

create table dealer (
  id int primary key not null,
  city varchar2(20) not null
);

create table car (
  id int primary key not null,
  brand varchar2(20),
  price int,
  dealer_id int references dealer (id)
);

create bitmap index bix1 on car (d.city, c.brand)
from car c, dealer d
where d.id = c.dealer_id;

select avg(c.price)
from dealer d
join car c on c.dealer_id = d.id
where d.city = 'Chicago' and c.brand = 'Buick';

sql server示例
sql server可以创建索引视图：

create table dealer (
  id int primary key not null,
  city varchar(20) not null
);

create table car (
  id int primary key not null,
  brand varchar(20),
  price int,
  dealer_id int references dealer (id)
);

create view v with schemabinding as
select d.city, c.brand, c.price, c.dealer_id
from dbo.dealer d
join dbo.car c on c.dealer_id = d.id;

create unique clustered index uix1 on v (city, brand, price);

select avg(c.price)
from dealer d
join car c on c.dealer_id = d.id
where d.city = 'Chicago' and c.brand = 'Buick';