making simple self join more efficent

Question

Hi,

I have a table

id|level|name

level can be 1,2 or 3

what I want to get is:

id|lvl1name|lvl2name|lvl3name

I'm using the following query

SELECT L1."name" as lvl1name, L2."name" as lvl2name, L3."name" as
lvl3name, L1.id
 FROM table as L1
       JOIN table as L2 ON L1.id = L2.id
       JOIN table as L3 ON L2.id = L3.id
       WHERE L1.lvl='1' and L2.lvl='2' and L3.lvl='3';

but it is soooooo slow!

there must be a better way to do this. please help

for this example I'm using postgres, but I'd be happy to learn some way that is not database feature dependant.

I can't write procedures (read only access), and I select this from a view.

Answer 1

Use:

  SELECT t.id,
         MAX(CASE WHEN t.level = 1 THEN t.name) AS level1name,
         MAX(CASE WHEN t.level = 2 THEN t.name) AS level2name,
         MAX(CASE WHEN t.level = 3 THEN t.name) AS level3name
    FROM YOUR_TABLE t
GROUP BY t.id

If you need this to be dynamic, you need to use dynamic SQL.