query returning multidimensional grouped arrays

Question

In the hypothetical scenario where I have a couple of database tables, in a one to many relationship. I am trying to find a nice query function so that I can return each row in table A with a nested array for all the linked rows from table B.

SELECT a.id AS id,a.name as name,b.id AS b_id,b.name AS b_name FROM a,b WHERE a.id=b.eid;

will return only one result

SELECT 
    a.id AS id,
    a.name as name,
    GROUP_CONCAT(b.id) AS b_id,
    GROUP_CONCAT(b.name) AS b_name 
FROM a,b 
WHERE a.id = b.eid;

whereas this returns what I want but I'm after an array not a string (there might be commas in b.name)

What am I missing?

Answer 1

You can use separator different from comma:

GROUP_CONCAT(b.name SEPARATOR ';') AS b_name

Answer 2

It isn't possible to return anything other than a MySQL datatype, so the short answer is no you cannot return a array (nested or otherwise) of results from a subquery. You'll also see some pretty drastic performance hits trying to build string concatenated values from the foreign, the sub-string order will be implicit and, as you've alluded to, you'll have problems selecting a suitable delimiter.

It almost certainly going to be more efficient use a simple JOIN to create a single result set. Any duplicates on the "one" side of the relationship should be handled programmatically (which is preferable, in any sense, to handling string splitting on multiple concatenated fields).