Re: Self-Join

Howdy, Abhinandan,

A quick and dirty solution might be this :

SELECT *
FROM
(
SELECT a.name,MAX(b.value) as height
FROM original a
LEFT JOIN original b
ON a.name = b.name
AND b.attribute = 'Height'
GROUP BY a.name
) height
NATURAL JOIN
(
SELECT a.name,MAX(b.value) as weigth
FROM original a
LEFT JOIN original b
ON a.name = b.name
AND b.attribute = 'Weight'
GROUP BY a.name
) weight
NATURAL JOIN
(
SELECT a.name,MAX(b.value) as age
FROM original a
LEFT JOIN
original
b
ON a.name = b.name
AND b.attribute = 'Age'
GROUP BY a.name
) age

The thing is that it doesn't scale well if you have many more items beyond three...

Best,
Oliveiros
----- Original Message -----
From: Abhinandan Raghavan
To: pgsql-sql(at)postgresql(dot)org
Sent: Tuesday, December 06, 2011 1:57 PM
Subject: [SQL] Self-Join

Hi,

I'm looking to frame an SQL statement in Postgres for what's explained in the attached image.

The original table is at the top and is called NAV (Short for Name, Attribute, Value). I want to create a view (NWHA_View) involving values from within (presumably from a self join). I would've normally created a view in the following way:

SELECT A.NAME,
A.VALUE AS WEIGHT,
B.VALUE AS HEIGHT,
C.VALUE AS AGE

FROM NAV A,
NAV B,
NAV C

WHERE A.NAME = B.NAME
AND A.NAME = C.NAME
AND A.ATTRIBUTE = 'Weight'
AND B.ATTRIBUTE = 'Height'
AND C.ATTRIBUTE = 'Age'

The only problem when I create a view with the above select statement is that when there are no entries for the field name "AGE" (in the case of David), then the row does not get displayed. What's the way out in Postgresql? I know the way it is addressed in Oracle but it doesn't seem to work in Postgresql.

Thanks.

Abhi

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