Use a GROUP_CONCAT and JOIN in a subquery - mysql

Question

I have a DB under MySQL with one main table with unique id, few tables that list different choices (with one id column, one text column to describe the item). So, for one record in the main table, I can have multiple choices associated to the choice table.
I'd like to create a View where all information could be visible, using GROUP_CONCAT to concatenate into one field the different choices from a given 'choice' table. However, my query repeats many times each list of choices when the record is related to other multiple choices from another 'choice' table. The query returns all the possible combinations between those choices...
Here my query (reduced to 2 'choice' tables -t_age, t_animal- for the example)
SELECT general.id_g,
GROUP_CONCAT(CAST(t_age AS CHAR) SEPARATOR ', ') AS age,
GROUP_CONCAT(CAST(t_animal AS CHAR) SEPARATOR ', ') AS animal
FROM general
LEFT JOIN interm_age
INNER JOIN t_age ON interm_age.id_age = t_age.id_age
ON general.id_g = interm_age.id_g
LEFT JOIN interm_animal
INNER JOIN t_animal ON interm_animal.id_animal = t_animal.id_animal
ON general.id_g = interm_animal.id_g
GROUP BY id_g;
I tried to include each CONCAT/JOIN within a subquery into a main SELECT as followed, but MySQL tells me "returns more than 1row", which is the case indeed. And?
SELECT id_g, (
SELECT GROUP_CONCAT(CAST(t_age AS CHAR) SEPARATOR ', ')
FROM general
LEFT JOIN interm_age
INNER JOIN t_age ON interm_age.id_age = t_age.id_age
ON general.id_g = interm_age.id_g
GROUP BY general.id_g )
FROM general;
[EDIT]
In more details, this is my DB (with FK)
general
-----------
id_g | date
902 | 2016/01/01
956 | 2016/02/01
959 | 2016/02/01
interm_age
-----------
id_age | id_g
1 | 902
3 | 902
1 | 956
4 | 956
interm_animal
-----------
id_animal | id_g
1 | 902
5 | 902
5 | 959
7 | 959
t_age
-----------
id_age | age
1 | <10y
3 | >10y
4 | >60y
t_animal
-----------
id_animal | animal
1 | bird
5 | mammal
7 | insect
And I would like something like :
id_g | date | age | animal
902 | 2016/01/01 | <10y, >10y | bird, mammal
and so on...
Thanks in advance!

Answer 1

Although it would be better if you provided some sample data, actual results, and expected results, I'll have a stab at the solution.
The issue probably is that you have multiple matching records in the joined tables, which leads to duplication of values within group_concat().
As MySQL documentation on group_concat() indicates, you can use the distinct keyword to remove duplicate values:
To eliminate duplicate values, use the DISTINCT clause.
SELECT general.id_g,
GROUP_CONCAT(DISTINCT CAST(t_age AS CHAR) SEPARATOR ', ') AS age,
GROUP_CONCAT(DISTINCT CAST(t_animal AS CHAR) SEPARATOR ', ') AS animal
FROM general
LEFT JOIN interm_age
INNER JOIN t_age ON interm_age.id_age = t_age.id_age
ON general.id_g = interm_age.id_g
LEFT JOIN interm_animal
INNER JOIN t_animal ON interm_animal.id_animal = t_animal.id_animal
ON general.id_g = interm_animal.id_g
GROUP BY id_g;

Answer 2

Try this
SELECT general.id_g,
GROUP_CONCAT(CAST(t_age AS CHAR) SEPARATOR ', ') AS age,
GROUP_CONCAT(CAST(t_animal AS CHAR) SEPARATOR ', ') AS animal
FROM general
LEFT JOIN interm_age
INNER JOIN t_age ON interm_age.id_age = t_age.id_age AND general.id_g = interm_age.id_g
LEFT JOIN interm_animal
INNER JOIN t_animal ON interm_animal.id_animal = t_animal.id_animal AND general.id_g = interm_animal.id_g
GROUP BY id_g;
Hope this helps.