plpg基础问题

tinghome

user_id integer;
quantity numeric(5);
url varchar;
myrow tablename%ROWTYPE;   
myfield tablename.fieldname%TYPE;
arow RECORD;

tablename%ROWTYPE是行类型的意思吗?
v_string ALIAS FOR $1是把v_string取别名为$1吗??
tablename.fieldname%TYPE是什么意思呢.
具体这些怎么用了.有没有简单点的??我看了PostgreSQL 8.0.0 文档
可是还是看不明白..初学.

joint

http://www.pgsqldb.org/pgsqldoc-8.0c/plpgsql.html

joint

--------------------------------
CREATE TABLE users (
id serial NOT NULL,
name character varying(32) NOT NULL
);
---------------------------------
CREATE TYPE user_set AS (
id integer,
name character varying(32)
);
---------------------------------
CREATE FUNCTION user_select_by_id("@id" int4)
RETURNS SETOF user_set
AS '
declare rec record;

begin

for rec in
select * from users where id = "@id"
loop
return next rec;
end loop;
return;

end; '
LANGUAGE plpgsql;
---------------------------------
CREATE FUNCTION user_delete_by_id("@id" int4)
RETURNS boolean
AS '
begin

delete from users where id = "@id"
return FOUND;

end; '
LANGUAGE plpgsql;
---------------------------------