How to concatenate strings of a string field in a PostgreSQL 'group by' query?

Question

I am looking for a way to concatenate the strings of a field within a group by query. So for example, I have a table:

ID   COMPANY_ID   EMPLOYEE
1    1               


        

Answer 1

I claim no credit for the answer because I found it after some searching:

What I didn't know is that PostgreSQL allows you to define your own aggregate functions with CREATE AGGREGATE

This post on the PostgreSQL list shows how trivial it is to create a function to do what's required:

CREATE AGGREGATE textcat_all(
  basetype    = text,
  sfunc       = textcat,
  stype       = text,
  initcond    = ''
);

SELECT company_id, textcat_all(employee || ', ')
FROM mytable
GROUP BY company_id;