postgresql - PostgreSQL : Composite types and select into

Question

谁能解释一下？ (一切都在下面的例子中!)。我使用 postgresql 9.4。警告!在下面的代码中，我删除了“对象类型”复合类型和“example_data”临时表，确保您的数据库中没有这些……以防万一，我注释掉了删除命令，如果需要则取消注释它们。 ..

--drop type if exists object_type;
--drop table if exists example_data;

create type object_type as (
       id text
       ,value text);

create temporary table example_data as (
       select
            'id1'::text as id,
            'example value'::text as value);

do $$
declare
    my_object object_type;
begin

    -- The fiolowing doesn't work, we can't use INTO with the whole object
    -- Some how, it tries to put the whole object into the first attribute:
    select (id,value)::object_type
    into my_object
    from example_data;

    raise warning 'ID: %, VALUE: %', my_object.id, my_object.value;

    -- What a shame! It would have been so much more convenient than the following:    
    -- to feed the object we need to repeat each one of the attribute in the INTO section:
    select id, value
    into  my_object.id, my_object.value
    from example_data;

    raise warning 'ID: %, VALUE: %', my_object.id, my_object.value;

/*
In that example it is not so bad, but when you have very large object, it is very ugly to repeat each one
of the attribute, for example:
select  (att1, att2, att3, att4, att5, att6, att7, att8, att9, att10)::object_type2 into my_object2

and, (very heavy):
select  att1, att2, att3, att4, att5, att6, att7, att8, att9, att10
into my_object2.att1, my_object2.att2, my_object2.att3, my_object2.att4, my_object2.att5, my_object2.att6,
     my_object2.att7, my_object2.att8, my_object2.att9, my_object2.att10

*/

end $$;

--drop type if exists object_type;
--drop table if exists example_data;

Answer 1

正在关注 the documentation:

...
select id, value
into my_object
from example_data;
...