From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Gauthier, Dave
Sent: Tuesday, October 23, 2012 2:53 PM
To: pgsql-general@postgresql.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.
