Loop in function does not work as expected - sql

Question

Using PostgreSQL 9.0.4
Below is a very similar structure of my table:
CREATE TABLE departamento
(
id bigserial NOT NULL,
master_fk bigint,
nome character varying(100) NOT NULL
CONSTRAINT departamento_pkey PRIMARY KEY (id),
CONSTRAINT departamento_master_fk_fkey FOREIGN KEY (master_fk)
REFERENCES departamento (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
And the function I created:
CREATE OR REPLACE FUNCTION fn_retornar_dptos_ate_raiz(bigint[])
RETURNS bigint[] AS
$BODY$
DECLARE
lista_ini_dptos ALIAS FOR $1;
dp_row departamento%ROWTYPE;
dpto bigint;
retorno_dptos bigint[];
BEGIN
BEGIN
PERFORM id FROM tbl_temp_dptos;
EXCEPTION
WHEN undefined_table THEN
EXECUTE 'CREATE TEMPORARY TABLE tbl_temp_dptos (id bigint NOT NULL) ON COMMIT DELETE ROWS';
END;
FOR i IN array_lower(lista_ini_dptos, 1)..array_upper(lista_ini_dptos, 1) LOOP
SELECT id, master_fk INTO dp_row FROM departamento WHERE id=lista_ini_dptos[i];
IF dp_row.id IS NOT NULL THEN
EXECUTE 'INSERT INTO tbl_temp_dptos VALUES ($1)' USING dp_row.id;
WHILE dp_row.master_fk IS NOT NULL LOOP
dpto := dp_row.master_fk;
SELECT id, master_fk INTO dp_row FROM departamento WHERE id=lista_ini_dptos[i];
EXECUTE 'INSERT INTO tbl_temp_dptos VALUES ($1)' USING dp_row.id;
END LOOP;
END IF;
END LOOP;
RETURN ARRAY(SELECT id FROM tbl_temp_dptos);
END;
$BODY$
LANGUAGE plpgsql VOLATILE
Any questions about the names I can translate ..
What is the idea of the function? I first check if the temporary table already exists (perform), and when the exception occurs I create a temporary table.
Then I take each element in the array and use it to fetch the id and master_fk of a department. If the search is successful (check if id is not null, it is even unnecessary) I insert the id in the temporary table and start a new loop.
The second loop is intended to get all parents of that department which was previously found by performing the previous steps (ie, pick a department and insert it into the temporary table).
At the end of the second loop returns to the first. When this one ends I return bigint[] refers to what was recorded in the temporary table.
My problem is that the function returns me the same list I provide. What am I doing wrong?

Answer 1

There is a lot I would do differently, and to great effect.
Table definition
Starting with the table definition and naming conventions. These are mostly just opinions:
CREATE TEMP TABLE conta (conta_id bigint primary key, ...);
CREATE TEMP TABLE departamento (
dept_id serial PRIMARY KEY
, master_id int REFERENCES departamento (dept_id)
, conta_id bigint NOT NULL REFERENCES conta (conta_id)
, nome text NOT NULL
);
Major points
Are you sure you need a bigserial for departments? There are hardly that many on this planet. A plain serial should suffice.
I hardly ever use character varying with a length restriction. Unlike with some other RDBMS there is no performance gain whatsoever by using a restriction. Add a CHECK constraint if you really need to enforce a maximum length. I just use text, mostly and save myself the trouble.
I suggest a naming convention where the foreign key column shares the name with the referenced column, so master_id instead of master_fk, etc. Also allows to use USING in joins.
And I rarely use the non-descriptive column name id. Using dept_id instead here.
PL/pgSQL function
It can be largely simplified to:
CREATE OR REPLACE FUNCTION f_retornar_plpgsql(lista_ini_depts VARIADIC int[])
RETURNS int[] AS
$func$
DECLARE
_row departamento; -- %ROWTYPE is just noise
BEGIN
IF NOT EXISTS ( -- simpler in 9.1+, see below
SELECT FROM pg_catalog.pg_class
WHERE relnamespace = pg_my_temp_schema()
AND relname = 'tbl_temp_dptos') THEN
CREATE TEMP TABLE tbl_temp_dptos (dept_id bigint NOT NULL)
ON COMMIT DELETE ROWS;
END IF;
FOR i IN array_lower(lista_ini_depts, 1) -- simpler in 9.1+, see below
.. array_upper(lista_ini_depts, 1) LOOP
SELECT * INTO _row -- since rowtype is defined, * is best
FROM departamento
WHERE dept_id = lista_ini_depts[i];
CONTINUE WHEN NOT FOUND;
INSERT INTO tbl_temp_dptos VALUES (_row.dept_id);
LOOP
SELECT * INTO _row
FROM departamento
WHERE dept_id = _row.master_id;
EXIT WHEN NOT FOUND;
INSERT INTO tbl_temp_dptos
SELECT _row.dept_id
WHERE NOT EXISTS (
SELECT FROM tbl_temp_dptos
WHERE dept_id =_row.dept_id);
END LOOP;
END LOOP;
RETURN ARRAY(SELECT dept_id FROM tbl_temp_dptos);
END
$func$ LANGUAGE plpgsql;
Call:
SELECT f_retornar_plpgsql(2, 5);
Or:
SELECT f_retornar_plpgsql(VARIADIC '{2,5}');
ALIAS FOR $1 is outdated syntax and discouraged. Use function parameters instead.
The VARIADIC parameter makes it more convenient to call. Related:
Pass multiple values in single parameter
You don't need EXECUTE for queries without dynamic elements. Nothing to gain here.
You don't need exception handling to create a table. Quoting the manual here:
Tip: A block containing an EXCEPTION clause is significantly more
expensive to enter and exit than a block without one. Therefore, don't
use EXCEPTION without need.
Postgres 9.1 or later has CREATE TEMP TABLE IF NOT EXISTS. I use a workaround for 9.0 to conditionally create the temp table.
Postgres 9.1 also offer FOREACH to loop through an arrays.
All that said, here comes the bummer: you don't need most of this.
SQL function with rCTE
Even in Postgres 9.0, a recursive CTE makes this a whole lot simpler:
CREATE OR REPLACE FUNCTION f_retornar_sql(lista_ini_depts VARIADIC int[])
RETURNS int[] AS
$func$
WITH RECURSIVE cte AS (
SELECT dept_id, master_id
FROM unnest($1) AS t(dept_id)
JOIN departamento USING (dept_id)
UNION ALL
SELECT d.dept_id, d.master_id
FROM cte
JOIN departamento d ON d.dept_id = cte.master_id
)
SELECT ARRAY(SELECT DISTINCT dept_id FROM cte) -- distinct values
$func$ LANGUAGE sql;
Same call.
Closely related answer with explanation:
Tree Structure and Recursion
SQL Fiddle demonstrating both.

Answer 2

I managed to fix my code. At the end of this response is its final form, but if you have any suggestions for improvement are welcome. Here are the changes:
1 - I have provided the essential structure of my table, but in reality it is much bigger. Before master_fk field, there is a field called account_fk, and because of the variable department dp_row%**ROWTYPE** the entire structure of my table is copied to the variable, so if I fill only the first two fields, i.e., id and account_fk, then master_fk that is the third field will be null.
2 - #Nicolas was right, and I ended up using the variable dpto for the second loop. And I had forgotten to fill it inside the loop. Besides using it in the search done within the loop.
3 - I added an if statement to make sure that would not have duplicates in the temporary table.
Correction in the structure of my table:
CREATE TABLE departamento
(
id bigserial NOT NULL,
account_fk bigint NOT NULL,
master_fk bigint,
nome character varying(100) NOT NULL,
CONSTRAINT departamento_pkey PRIMARY KEY (id),
CONSTRAINT departamento_account_fk_fkey FOREIGN KEY (account_fk)
REFERENCES conta (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT departamento_master_fk_fkey FOREIGN KEY (master_fk)
REFERENCES departamento (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
My function as it is now:
CREATE OR REPLACE FUNCTION fn_retornar_dptos_ate_raiz(bigint[]) RETURNS bigint[] AS
$BODY$
DECLARE
lista_ini_dptos ALIAS FOR $1;
dp_row departamento%ROWTYPE;
dpto bigint;
BEGIN
BEGIN
PERFORM id FROM tbl_temp_dptos;
EXCEPTION
WHEN undefined_table THEN
EXECUTE 'CREATE TEMPORARY TABLE tbl_temp_dptos (id bigint NOT NULL) ON COMMIT DELETE ROWS';
END;
FOR i IN array_lower(lista_ini_dptos, 1)..array_upper(lista_ini_dptos, 1) LOOP
SELECT id, conta_fk, master_fk INTO dp_row FROM departamento WHERE id=lista_ini_dptos[i];
EXECUTE 'INSERT INTO tbl_temp_dptos VALUES ($1)' USING dp_row.id;
dpto := dp_row.master_fk;
-- RAISE NOTICE 'dp_row: (%); ', dp_row.master_fk;
WHILE dpto IS NOT NULL LOOP
SELECT id, conta_fk, master_fk INTO dp_row FROM departamento WHERE id=dpto;
IF NOT(select exists(select 1 from tbl_temp_dptos where id=dp_row.id limit 1)) THEN
EXECUTE 'INSERT INTO tbl_temp_dptos VALUES ($1)' USING dp_row.id;
END IF;
dpto := dp_row.master_fk;
-- RAISE NOTICE 'dp_row: (%); ', dp_row.master_fk;
END LOOP;
END LOOP;
RETURN ARRAY(SELECT id FROM tbl_temp_dptos);
END;
$BODY$
LANGUAGE plpgsql VOLATILE