making simple self join more efficent
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 happ开发者_Python百科y 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.
Use:
SELECT t.id,
MAX(CASE WHEN t.level = 1 THEN t.name END) AS level1name,
MAX(CASE WHEN t.level = 2 THEN t.name END) AS level2name,
MAX(CASE WHEN t.level = 3 THEN t.name END) AS level3name
FROM YOUR_TABLE t
GROUP BY t.id
If you need this to be dynamic, you need to use dynamic SQL.
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