skyeagle skyeagle - 1 month ago 18
SQL Question

Return multiple fields as a record in PostgreSQL with PL/pgSQL

I am writing a SP, using PL/pgSQL.

I want to return a record, comprised of fields from several different tables. Could look something like this:

CREATE OR REPLACE FUNCTION get_object_fields(name text)
RETURNS RECORD AS $$
BEGIN
-- fetch fields f1, f2 and f3 from table t1
-- fetch fields f4, f5 from table t2
-- fetch fields f6, f7 and f8 from table t3
-- return fields f1 ... f8 as a record
END
$$ language plpgsql;


How may I return the fields from different tables as fields in a single record?

[Edit]

I have realized that the example I gave above was slightly too simplistic. Some of the fields I need to be retrieving, will be saved as separate rows in the database table being queried, but I want to return them in the 'flattened' record structure.

The code below should help illustrate further:

CREATE TABLE user (id int, school_id int, name varchar(32));

CREATE TYPE my_type (
user1_id int,
user1_name varchar(32),
user2_id int,
user2_name varchar(32)
);

CREATE OR REPLACE FUNCTION get_two_users_from_school(schoolid int)
RETURNS my_type AS $$
DECLARE
result my_type;
temp_result user;
BEGIN
-- for purpose of this question assume 2 rows returned
SELECT id, name INTO temp_result FROM user where school_id = schoolid LIMIT 2;
-- Will the (pseudo)code below work?:
result.user1_id := temp_result[0].id ;
result.user1_name := temp_result[0].name ;
result.user2_id := temp_result[1].id ;
result.user2_name := temp_result[1].name ;
return result ;
END
$$ language plpgsql

Answer

You need to define a new type and define your function to return that type.

CREATE TYPE my_type AS (f1 varchar(10), f2 varchar(10) /* , ... */ );

CREATE OR REPLACE FUNCTION get_object_fields(name text) 
RETURNS my_type 
AS 
$$

DECLARE
  result_record my_type;

BEGIN
  SELECT f1, f2, f3
  INTO result_record.f1, result_record.f2, result_record.f3
  FROM table1
  WHERE pk_col = 42;

  SELECT f3 
  INTO result_record.f3
  FROM table2
  WHERE pk_col = 24;

  RETURN result_record;

END
$$ LANGUAGE plpgsql; 

If you want to return more than one record you need to define the function as returns setof my_type


Update

Another option is to use RETURNS TABLE() instead of creating a TYPE which was introduced in Postgres 8.4

CREATE OR REPLACE FUNCTION get_object_fields(name text) 
  RETURNS TABLE (f1 varchar(10), f2 varchar(10) /* , ... */ )
...