Postgres colpivot function return nothing - postgresql

Question

I try to follow this tutorial http://www.anhuiyouxi.com/transposing-an-sql-result-so-that-one-column-goes-onto-multiple-columns/. I do it by run below code:
CREATE EXTENSION IF NOT EXISTS tablefunc;
create or replace function colpivot(
out_table varchar, in_query varchar,
key_cols varchar[], class_cols varchar[],
value_e varchar, col_order varchar
) returns void as $$
declare
in_table varchar;
col varchar;
ali varchar;
on_e varchar;
i integer;
rec record;
query varchar;
-- This is actually an array of arrays but postgres does not support an array of arrays type so we flatten it.
-- We could theoretically use the matrix feature but it's extremly cancerogenous and we would have to involve
-- custom aggrigates. For most intents and purposes postgres does not have a multi-dimensional array type.
clsc_cols text[] := array[]::text[];
n_clsc_cols integer;
n_class_cols integer;
begin
in_table := quote_ident('__' || out_table || '_in');
execute ('create temp table ' || in_table || ' on commit drop as ' || in_query);
-- get ordered unique columns (column combinations)
query := 'select array[';
i := 0;
foreach col in array class_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || 'quote_literal(' || quote_ident(col) || ')';
i := i + 1;
end loop;
query := query || '] x from ' || in_table;
for j in 1..2 loop
if j = 1 then
query := query || ' group by ';
else
query := query || ' order by ';
if col_order is not null then
query := query || col_order || ' ';
exit;
end if;
end if;
i := 0;
foreach col in array class_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || quote_ident(col);
i := i + 1;
end loop;
end loop;
-- raise notice '%', query;
for rec in
execute query
loop
clsc_cols := array_cat(clsc_cols, rec.x);
end loop;
n_class_cols := array_length(class_cols, 1);
n_clsc_cols := array_length(clsc_cols, 1) / n_class_cols;
-- build target query
query := 'select ';
i := 0;
foreach col in array key_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || '_key.' || quote_ident(col) || ' ';
i := i + 1;
end loop;
for j in 1..n_clsc_cols loop
query := query || ', ';
col := '';
for k in 1..n_class_cols loop
if k > 1 then
col := col || ', ';
end if;
col := col || clsc_cols[(j - 1) * n_class_cols + k];
end loop;
ali := '_clsc_' || j::text;
query := query || '(' || replace(value_e, '#', ali) || ')' || ' as ' || quote_ident(col) || ' ';
end loop;
query := query || ' from (select distinct ';
i := 0;
foreach col in array key_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || quote_ident(col) || ' ';
i := i + 1;
end loop;
query := query || ' from ' || in_table || ') _key ';
for j in 1..n_clsc_cols loop
ali := '_clsc_' || j::text;
on_e := '';
i := 0;
foreach col in array key_cols loop
if i > 0 then
on_e := on_e || ' and ';
end if;
on_e := on_e || ali || '.' || quote_ident(col) || ' = _key.' || quote_ident(col) || ' ';
i := i + 1;
end loop;
for k in 1..n_class_cols loop
on_e := on_e || ' and ';
on_e := on_e || ali || '.' || quote_ident(class_cols[k]) || ' = ' || clsc_cols[(j - 1) * n_class_cols + k];
end loop;
query := query || 'left join ' || in_table || ' as ' || ali || ' on ' || on_e || ' ';
end loop;
-- raise notice '%', query;
execute ('create temp table ' || quote_ident(out_table) || ' on commit drop as ' || query);
-- cleanup temporary in_table before we return
execute ('drop table ' || in_table)
return;
end;
$$ language plpgsql volatile;
begin;
DROP TABLE IF EXISTS qa;
create temp table qa (id int, usr int, question_id int, answer_id int);
insert into qa values
(1,1,1,1)
,(2,1,2,9)
,(3,1,3,15)
,(4,2,1,2)
,(5,2,2,12)
,(6,2,3,20);
--select * from qa;
select colpivot('_output', $$
select usr, ('q' || question_id::text) question_id, answer_id from qa
$$, array['usr'], array['question_id'], '#.answer_id', null);
select * from _output;
rollback;
After reach to the end line of the code, I got nothing.
Am I doing it wrong?
Please advise

Answer 1

I've changed the function a little bit, you can do a diff to see exactly what, but it seems like the function is dropping the result table at the end (i'm assuming it does a commit, so drops it). I've added a drop of the temp table incase it already exists. Also I removed the quote_ident() function calls around the table names as that was causing a problem when passing across a long table name value for out_table (on ver 9.6).
-- Copyright © 2015, Hannes Landeholm <hannes#jumpstarter.io>
-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
-- See the README.md file distributed with this project for documentation.
create or replace function colpivot(
out_table varchar, in_query varchar,
key_cols varchar[], class_cols varchar[],
value_e varchar, col_order varchar
) returns void as $$
declare
in_table varchar;
col varchar;
ali varchar;
on_e varchar;
i integer;
rec record;
query varchar;
-- This is actually an array of arrays but postgres does not support an array of arrays type so we flatten it.
-- We could theoretically use the matrix feature but it's extremly cancerogenous and we would have to involve
-- custom aggrigates. For most intents and purposes postgres does not have a multi-dimensional array type.
clsc_cols text[] := array[]::text[];
n_clsc_cols integer;
n_class_cols integer;
begin
in_table := ('__' || out_table || '_in');
-- if the temp table already exists, drop
execute ( 'drop TABLE IF EXISTS ' || in_table );
execute ('create temp table ' || in_table || ' on commit drop as ' || in_query);
-- get ordered unique columns (column combinations)
query := 'select array[';
i := 0;
foreach col in array class_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || 'quote_literal(' || quote_ident(col) || ')';
i := i + 1;
end loop;
query := query || '] x from ' || in_table;
for j in 1..2 loop
if j = 1 then
query := query || ' group by ';
else
query := query || ' order by ';
if col_order is not null then
query := query || col_order || ' ';
exit;
end if;
end if;
i := 0;
foreach col in array class_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || quote_ident(col);
i := i + 1;
end loop;
end loop;
-- raise notice '%', query;
for rec in
execute query
loop
clsc_cols := array_cat(clsc_cols, rec.x);
end loop;
n_class_cols := array_length(class_cols, 1);
n_clsc_cols := array_length(clsc_cols, 1) / n_class_cols;
-- build target query
query := 'select ';
i := 0;
foreach col in array key_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || '_key.' || quote_ident(col) || ' ';
i := i + 1;
end loop;
for j in 1..n_clsc_cols loop
query := query || ', ';
col := '';
for k in 1..n_class_cols loop
if k > 1 then
col := col || ', ';
end if;
col := col || clsc_cols[(j - 1) * n_class_cols + k];
end loop;
ali := '_clsc_' || j::text;
query := query || '(' || replace(value_e, '#', ali) || ')' || ' as ' || quote_ident(col) || ' ';
end loop;
query := query || ' from (select distinct ';
i := 0;
foreach col in array key_cols loop
if i > 0 then
query := query || ', ';
end if;
query := query || quote_ident(col) || ' ';
i := i + 1;
end loop;
query := query || ' from ' || in_table || ') _key ';
for j in 1..n_clsc_cols loop
ali := '_clsc_' || j::text;
on_e := '';
i := 0;
foreach col in array key_cols loop
if i > 0 then
on_e := on_e || ' and ';
end if;
on_e := on_e || ali || '.' || quote_ident(col) || ' = _key.' || quote_ident(col) || ' ';
i := i + 1;
end loop;
for k in 1..n_class_cols loop
on_e := on_e || ' and ';
on_e := on_e || ali || '.' || quote_ident(class_cols[k]) || ' = ' || clsc_cols[(j - 1) * n_class_cols + k];
end loop;
query := query || 'left join ' || in_table || ' as ' || ali || ' on ' || on_e || ' ';
end loop;
-- raise notice '%', query;
execute ('create temp table ' || out_table || ' as ' || query);
-- cleanup temporary in_table before we return
execute ('drop table ' || in_table);
return;
end;
$$ language plpgsql volatile;
Now you can run it like so:
DROP TABLE IF EXISTS qa;
create temp table qa (id int, usr int, question_id int, answer_id int);
insert into qa values
(1,1,1,1)
,(2,1,2,9)
,(3,1,3,15)
,(4,2,1,2)
,(5,2,2,12)
,(6,2,3,20);
--select * from qa;
select colpivot('_output', $$
select usr, ('q' || question_id::text) question_id, answer_id from qa
$$, array['usr'], array['question_id'], '#.answer_id', null);
-- then run the select to get the result
select * from _output;