Select all related records when using group by in mySQL?

Question

So I have table A and B

Obejcts
 - id
 - someId
 ...

TableB
 - table_A_Id

So A has one to many relationship with B.

I wanna select from Table A grouped by someId left joining Table B. However if I do that, only one row is returned for each item selected from Table A. Can I get all records from table B for each record of A or does this require two queries?

So I want something like this:

 - TableARecord1
    RelatedTableBrecord1
    RelatedTableBrecord2

But because of the grouping, this is what I get:

 - TableARecord1
    RelatedTableBrecord1

Can I do this with MySQL 5.x?

EDIT:

The tables are huge and the query is generated by an ORM so it's also huge, but basically I'm doing this:

SELECT table1.id, COUNT(DISTINCT(table1.someId)) as counter, table2.instanceId FROM table1 LEFT JOIN table2 ON table1.id=table2.table1Id GROUP BY table1.someId

This returns records like this:

{
id: 1,
counter: 10,
relatedItemsFromTable2: [
 instanceId
]
}

The array always has 1 item. But there are more, should be:

{
id: 1,
counter: 10,
relatedItemsFromTable2: [
 instanceId,
 instanceId2,
 instanceId3
]
}

I'm not sure if this is enough info. If not, please let me know and I'll post some simplified example tables and query.