Informix one to many format issue - informix

Question

Trying to fix my Informix query results format from a one to many relationship. My current query is using a JOIN but is creating a new line for every time there is a match to the JOIN ON condition. I should add the below is only an example, the real data is thousands of entries with about a 100 unique "category" entries so I cant hard code WHERE statements, it needs to read each entry and add if a match. I tried a GROUP_CONCAT however is just returned an error, guess its not a informix function, I also tried reading this thread but have yet been unable to get working. Show a one to many relationship as 2 columns - 1 unique row (ID & comma separated list)
Any help will be appreciated.
IBM/Informix-Connect Version 3.70.UC4
IBM/Informix LIBGLS LIBRARY Version 5.00.UC5
IBM Informix Dynamic Server Version 11.70.FC8W1
Tables
movie
name rating movie_id
rio g 1
horton g 2
blade r 3
lotr_1 pg13 4
lotr_2 pg13 5
paul_blart pg 6
category
cat_name id
kids 1
comedy 2
action 3
fantasy 4
category_member
movie_name cat_name catmem_id
lotr_1 action 1
lotr_1 fantasy 2
rio kids 3
rio comedy 4
When I use
#!/bin/bash
echo "SET isolation dirty read;
UNLOAD to /export/home/movie/movieDetail.unl DELIMITER ','
SELECT a.name, a.rating, b.cat_name
FROM movie a
LEFT JOIN category b ON b.movie_name = a.name
;" | dbaccess thedb;
What I get is
rio,g,kids
rio,g,comedy
lotr_1,pg13,action
lotr_1,pg13,fantasy
What I would like is
rio,g,kids,comedy
lotr_1,pg13,action,fantasy

Answer 1

Install the GROUP_CONCAT user-defined aggregate
You must install the GROUP_CONCAT user-defined aggregate from SO 715350 (referenced in your question) into your database. The GROUP_CONCAT aggregate is not defined by Informix, but can be added if you use the SQL from that question. One difference between that and a normal built-in function is that you need to install the aggregate in each database in the server where you need to use it. There might be a way to do a 'global install' (for all databases in a given server), but I've forgotten (or, more accurately, never learned) how to do it.
Writing your queries
With the sample database listed at the bottom:
The query in the question does not run:
SELECT a.name, a.rating, b.cat_name
FROM movie a
LEFT JOIN category b ON b.movie_name = a.name;
SQL -217: Column (movie_name) not found in any table in the query (or SLV is undefined).
This can be fixed by changing category to category_member. This produces:
SELECT a.name, a.rating, b.cat_name
FROM movie a
LEFT JOIN category_member b ON b.movie_name = a.name;
rio g kids
rio g comedy
horton g
blade r
lotr_1 pg13 action
lotr_1 pg13 fantasy
lotr_2 pg13
paul_blart pg
The LEFT JOIN appears to be unwanted. And using GROUP_CONCAT produces approximately the desired answer:
SELECT a.name, a.rating, GROUP_CONCAT(b.cat_name)
FROM movie a
JOIN category_member b ON b.movie_name = a.name
GROUP BY a.name, a.rating;
rio g kids,comedy
lotr_1 pg13 action,fantasy
If you specify the delimiter as ,, the commas in the data from the GROUP_CONCAT operator will be escaped to avoid ambiguity:
SELECT a.NAME, a.rating, GROUP_CONCAT(b.cat_name)
FROM movie a
JOIN category_member b ON b.movie_name = a.NAME
GROUP BY a.NAME, a.rating;
rio,g,kids\,comedy
lotr_1,pg13,action\,fantasy
Within standard Informix utilities, there isn't a way to avoid that; they don't leave the selected/unloaded data in an ambiguous format.
I'm not convinced that the database schema is very well organized. The Movie table is OK; the Category table is OK; but the Category_Member table would be more orthodox if it used the schema:
DROP TABLE IF EXISTS category_member;
CREATE TABLE category_member
(
movie_id INTEGER NOT NULL REFERENCES Movie(Movie_id),
category_id INTEGER NOT NULL REFERENCES Category(Id),
PRIMARY KEY(movie_id, category_id)
);
INSERT INTO category_member VALUES(4, 3);
INSERT INTO category_member VALUES(4, 4);
INSERT INTO category_member VALUES(1, 1);
INSERT INTO category_member VALUES(1, 2);
-- Use GROUP_CONCAT
SELECT a.NAME, a.rating, GROUP_CONCAT(c.cat_name)
FROM movie a
JOIN category_member b ON b.movie_id = a.movie_id
JOIN category c ON b.category_id = c.id
GROUP BY a.NAME, a.rating;
The output from this query is the same as from the previous one, but the joining is more orthodox.
Sample database
DROP TABLE IF EXISTS movie;
CREATE TABLE movie
(
name VARCHAR(20) NOT NULL UNIQUE,
rating CHAR(4) NOT NULL,
movie_id SERIAL NOT NULL PRIMARY KEY
);
INSERT INTO movie VALUES("rio", "g", 1);
INSERT INTO movie VALUES("horton", "g", 2);
INSERT INTO movie VALUES("blade", "r", 3);
INSERT INTO movie VALUES("lotr_1", "pg13", 4);
INSERT INTO movie VALUES("lotr_2", "pg13", 5);
INSERT INTO movie VALUES("paul_blart", "pg", 6);
DROP TABLE IF EXISTS category;
CREATE TABLE category
(
cat_name VARCHAR(10) NOT NULL UNIQUE,
id SERIAL NOT NULL PRIMARY KEY
);
INSERT INTO category VALUES("kids", 1);
INSERT INTO category VALUES("comedy", 2);
INSERT INTO category VALUES("action", 3);
INSERT INTO category VALUES("fantasy", 4);
DROP TABLE IF EXISTS category_member;
CREATE TABLE category_member
(
movie_name VARCHAR(20) NOT NULL,
cat_name VARCHAR(10) NOT NULL,
catmem_id SERIAL NOT NULL PRIMARY KEY
);
INSERT INTO category_member VALUES("lotr_1", "action", 1);
INSERT INTO category_member VALUES("lotr_1", "fantasy", 2);
INSERT INTO category_member VALUES("rio", "kids", 3);
INSERT INTO category_member VALUES("rio", "comedy", 4);