POSTGRESQL-查询没有结果数据的目的地

Question

我是postgres和编程的新手,我已经为此寻找解决方案,但我无法理解.我正在尝试创建一个函数,只要我呼叫该国家,就会返回有关该特定国家/地区所有客户的信息.这是弹出的错误.我真的很抱歉这个问题,但我从昨天开始就被困在这里.

错误:查询没有结果数据的目的地
提示:如果要丢弃SELECT的结果,请改用PERFORM.
语境:SQL语句中的PL/pgSQL函数country(text)第5行

这是功能:

create or replace function country(text) returns text as $$
begin


  select customer_id, customer.first_name, customer.last_name 

  from customer 

  inner join address on customer.address_id = address.address_id 
  inner join city on address.city_id = city.city_id 
  inner join country on city.country_id = country.country_id 

  where country = '$1';
  end;
  $$

  language plpgsql;

Answer 1

如果在PL/pgSQL函数中执行select语句,则应将查询结果放在某个变量(=目标)中.然后使用函数中的变量.你还应该有一份RETURN声明.

create or replace function country(text) returns text as $$
declare                   -- declare some variables
  id integer;
  fname text;
  lname text;
begin
  select customer_id, customer.first_name, customer.last_name 
    into id, fname, lname -- store query results in variables
  from customer 
  inner join address on customer.address_id = address.address_id 
  inner join city on address.city_id = city.city_id 
  inner join country on city.country_id = country.country_id 
  where country = $1;     -- don't quote parameter references

  -- do something with the variables and return a value from the function
  return format('%s: %s %s', id, upper(lname), fname);
end;
$$ language plpgsql;

请注意,只有在查询返回单行时,上述操作才有效.如果查询返回多行,则可以在函数中使用循环.更简单的是,您可以从查询中返回结果,如下所示:

create or replace function country(text)
returns table (id integer, first_name varchar, last_name varchar) as $$
begin
  return query
    select customer_id, customer.first_name, customer.last_name 
    from customer 
    inner join address on customer.address_id = address.address_id 
    inner join city on address.city_id = city.city_id 
    inner join country on city.country_id = country.country_id 
    where country = $1;
end;
$$ language plpgsql;

但是就像Evan Carroll所说的那样,除非你需要PL/pgSQL函数来修改数据才能返回它,你最好用一个简单的视图.