PostgreSQL 9.1: How to concatenate rows in array without duplicates, JOIN another table

Question

I am using PostgreSQL 9.1 and need help with concatenating multiple rows in one. I need to do that in 2 tables. When I use two times array_agg() functions I get

Answer 1

Instead of using window functions and patitioning, use a query-level GROUP BY and aggregate with a DISTINCT clause:

SELECT         
  rnp.grp_id,
  array_to_string(array_agg(distinct rnp.cabinets),',') AS cabinets,
  array_to_string(array_agg(distinct ips.address),',')  AS addresses
FROM rnp JOIN ips ON rnp.grp_id=ips.grp_id GROUP BY rnp.grp_id, ips.grp_id;

Result:

 grp_id |        cabinets         | addresses 
--------+-------------------------+-----------
     11 | cabs1,cabs2,cabs3,cabs4 | CA,NY
     22 | c1,c2                   | DC,LA
(2 rows)

The key here is that instead of using window functions and patitioning, you use a query-level GROUP BY and aggregate with a DISTINCT clause.

This'd work with the window function approach too, except that PostgreSQL (9.1 at least) doesn't support DISTINCT in window functions:

regress=# SELECT DISTINCT
  rnp.grp_id,
  array_to_string(array_agg(distinct rnp.cabinets)OVER (PARTITION BY rnp.grp_id), ',') AS cabinets,                    
  array_to_string(array_agg(distinct ips.address) OVER (PARTITION BY ips.grp_id), ',') AS addresses
FROM rnp JOIN ips ON rnp.grp_id=ips.grp_id;
ERROR:  DISTINCT is not implemented for window functions
LINE 3:   array_to_string(array_agg(distinct rnp.cabinets)OVER (PART...