Re: Need sql to pull data from terribly architected table

From: pgsql-general-owner(at)postgresql(dot)org
[mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of Gauthier, Dave
Sent: Tuesday, October 23, 2012 2:53 PM
To: pgsql-general(at)postgresql(dot)org
Subject: [GENERAL] Need sql to pull data from terribly architected table

Here's the deal...

Instead of architecting and loading a table like...

create teble foo (col1 text, col2 text, col3 text, col4 text, col5 text);

insert into foo (col1,col2,col3,col4,col5) values
('c1',null,'c3','c4',null);

They did this instead...

create table foo (property text, value text);

insert into foo (property, value) values ('col1','c1'), ('col3','c3'),
('col4','c4');

Notice how "col2" and "col5" were simply left out of the table in the 2nd
model to indicate null.

The question is how to do this model 1 query for model 2...

select col1,col2 from foo where col4='c4' and col5 <> 'xxx';

I know I have to use outer joins to deal with the potential of nulls. But I
don't know how to construct this. I won't list my failed attempts (so as
not to embarass myself :-))

Thanks in Advance !

WITH remap (

SELECT id_field_not_shown_above, v1, v2, v3, v4, v5

FROM (SELECT id_field_not_shown_above FROM foo) master

LEFT JOIN (SELECT id_field_not_shown_above, v1 FROM foo WHERE property =
'col1') r1 USING (id_field_not_shown_above)

LEFT JOIN (SELECT id_field_not_shown_above, v2 FROM foo WHERE property =
'col2') r2 USING (id_field_not_shown_above)

LEFT JOIN (SELECT id_field_not_shown_above, v3 FROM foo WHERE property =
'col3') r3 USING (id_field_not_shown_above)

LEFT JOIN (SELECT id_field_not_shown_above, v4 FROM foo WHERE property =
'col4') r4 USING (id_field_not_shown_above)

LEFT JOIN (SELECT id_field_not_shown_above, v5 FROM foo WHERE property =
'col5') r5 USING (id_field_not_shown_above)

)

SELCET * FROM remap

David J.