SQL – consolidate rows after SELECT CASE statement

Question

I want to consolidate rows with matching IDs returning from a SELECT CASE statement. I'm using pgAdmin 3 on a PG-9.3.4 database.

This is what I'm getting on pgAdmin:

And this is what I want to get:

I've tried grouping it, or joining the result to the table itself, but din't work. Any ideas?

My query code:

SELECT
    CASE
    WHEN t1.material LIKE '%Refuse%'
        THEN t1.disposal
    ELSE NULL
END AS msw_disp,

    CASE
    WHEN t1.material LIKE '%Met%'
        THEN t1.disposal
    ELSE NULL
END AS mgp_disp,

    CASE
    WHEN t1.material LIKE '%Paper%'
        THEN t1.disposal
    ELSE NULL
END AS pap_disp, t1.district

FROM dsny_net t1

Answer 1

Adding Aggregate and Group by to your current query should get the job done

SELECT Max(CASE 
             WHEN t1.material LIKE '%Refuse%' THEN t1.disposal 
           END) AS msw_disp, 
       Max(CASE 
             WHEN t1.material LIKE '%Met%' THEN t1.disposal 
           END) AS mgp_disp, 
       Max(CASE 
             WHEN t1.material LIKE '%Paper%' THEN t1.disposal 
           END) AS pap_disp, 
       t1.district 
FROM   dsny_net t1 
GROUP  BY t1.district 

Answer 2

Just as alternative:

select
  district,
  unnest(array_agg(disposal) filter (where material like '%Refuse%')) as msw_disp,
  unnest(array_agg(disposal) filter (where material like '%Met%')) as mgp_disp,
  unnest(array_agg(disposal) filter (where material like '%Paper%')) as pap_disp,
from dsny_net
group by district;

Using max will drops all other values (if any) except max.

However unnest(array_agg(disposal) filter (where material like ...)) as ... can be replaced by max(disposal) filter (where material like ...) as.. to make query shorter.