带有生成列的 PostgreSQL 查询

我有一个如下所示的架构，我想运行一个查询，在输出中为每一行获取一列points table.

所以对于每个usage我想乘以行amount使用次数的amount对于引用的points_id，然后总结并按人分组。因此，对于示例数据，我希望输出如下所示：

 Name  | foo  | bar  | baz  
-------|------|------|------
 Scott | 10.0 | 24.0 | 0.0  
 Sam   | 0.0  | 0.0  | 46.2   

这是架构/数据：

CREATE TABLE points (
   ident int primary key NOT NULL,
   abbrev VARCHAR NOT NULL,
   amount real NOT NULL
);

CREATE TABLE usage (
  ident int primary key NOT NULL,
  name VARCHAR NOT NULL,
  points_id integer references points (ident),
  amount real
);

INSERT INTO points (ident, abbrev, amount) VALUES
  (1, 'foo', 1.0),
  (2, 'bar', 2.0),
  (3, 'baz', 3.0);

INSERT INTO usage (ident, name, points_id, amount) VALUES 
  (1, 'Scott', 1, 10),
  (2, 'Scott', 2, 12),
  (3, 'Sam', 3, 3.4),
  (4, 'Sam', 3, 12);

我正在使用 PostgreSQL 9.2.8

数据只是样本。真实的有几千行usage桌子上可能有十几个points桌子。这里的真正意图是我不想硬编码所有points我在许多函数中使用它们时求和。

select 
t1.name,
sum(case when t2.abbrev='foo' then t1.amount*t2.amount else 0 end) as foo,
sum(case when t2.abbrev='bar' then t1.amount*t2.amount else 0 end) as bar,
sum(case when t2.abbrev='baz' then t1.amount*t2.amount else 0 end) as baz
from usage t1 inner join points t2 on t1.points_id=t2.ident
group by t1.name;

SQL 小提琴示例：http://sqlfiddle.com/#!15/cc84a/6 http://sqlfiddle.com/#!15/cc84a/6;

对于动态情况，使用以下 PostgreSQL 函数：

create or replace function sp_test()
returns void as
$$

declare cases character varying;
declare sql_statement text;
begin

select string_agg(concat('sum(case when t2.abbrev=','''',abbrev,'''',' then t1.amount*t2.amount else 0 end) as ', abbrev),',') into cases from points;

drop table if exists temp_data;

sql_statement=concat('create temporary table temp_data as select 
t1.name,',cases ,' 
from usage t1 inner join points t2 on t1.points_id=t2.ident
group by t1.name ');

execute sql_statement;

end;
$$
language 'plpgsql';

函数使用临时表来存储动态列数据。

通过以下方式调用函数来获取数据：

select * from sp_test(); select * from temp_data;