Combining rows to create two columns of data - sql

Question

I'm a bit confused on how to do this query properly. I have a table that looks like this. Where district 0 represent a value that should be applied to all district (global).
[ district ] [ code ] [ value ]
1 A 11
1 C 12
2 A 13
2 B 14
0 B 15
I have built a query (below) to combine the "global value" on each district.
[ district ] [ code ] [ district value ] [ global value ]
1 A 11 null -> row 1
1 B null 15 -> row 2
1 C 12 null -> row 3
2 A 13 null -> row 4
2 B 14 15 -> row 5
2 C null null -> row 6 (optional)
I did it by joining on the list of all possible district/code.
select all_code.district, all_code.code, table_d.value, table_g.value
from (select distinct b.district, a.code
from temp_table a
inner join (select distinct district
from temp_table
where district <> 0) b
on 1 = 1) all_code
left join temp_table table_d
on table_d.code = all_code.code
and table_d.district = all_code.district
left join temp_table table_g
on table_g.code = all_code.code
and table_g.district = 0
This query works great but seems pretty ugly. Is there a better way of doing this? (note that I don't care if row #6 is there or not).
Here's a script if needed.
create table temp_table
(
district VARCHAR2(5) not null,
code VARCHAR2(5) not null,
value VARCHAR2(5) not null
);
insert into temp_table (district, code, value)
values ('1', 'A', '11');
insert into temp_table (district, code, value)
values ('1', 'C', '12');
insert into temp_table (district, code, value)
values ('2', 'A', '13');
insert into temp_table (district, code, value)
values ('2', 'B', '14');
insert into temp_table (district, code, value)
values ('0', 'B', '15');

Answer 1

Here is one of the options. Since you are on 10g you can make use of partition outer join(partition by() clause) to fill the gaps:
with DCodes(code) as(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual
),
DGlobal(code, value1) as(
select code
, value
from temp_table
where district = 0
)
select tt.district
, dc.code
, tt.value
, dg.value1 as global_value
from temp_table tt
partition by(tt.district)
right join DCodes dc
on (dc.code = tt.code)
left join DGlobal dg
on (dg.code = dc.code)
where tt.district != 0
order by 1, 2
Result:
DISTRICT CODE VALUE GLOBAL_VALUE
-------- ---- ----- ------------
1 A 11
1 B 15
1 C 12
2 A 13
2 B 14 15
2 C

Answer 2

I would argue that a lot of the "ugliness" comes from a lack of lookup tables for district and code. Without an authoritative source for those, you have to fabricate one from the values that are in use (hence the sub-queries with distinct).
In terms of cleaning up the query you have, the best I can come up with is to remove an unnecessary sub-query and use the proper syntax for the cross join:
SELECT a.district,
b.code,
c.value1,
d.value1
FROM (SELECT DISTINCT district FROM temp_table WHERE district <> 0) a
CROSS JOIN (SELECT DISTINCT code FROM temp_table) b
LEFT JOIN temp_table c
ON b.code = c.code AND a.district = c.district
LEFT JOIN temp_table d
ON b.code = d.code AND d.district = 0
ORDER BY district, code