Case statement with four columns, i.e. attributes - sql

Question

I have a table with values "1", "0" or "". The table has four columns: p, q, r and s.
I need help creating a case statement that returns values when the attribute is equal to 1.
For ID 5 the case statement should return "p s".
For ID 14 the case statement should return "s".
For ID 33 the case statement should return 'p r s". And so on.
Do I need to come with a case statement that has every possible combination? Or is there a simpler way. Below is what I have come up with thus far.
case
when p = 1 and q =1 then "p q"
when p = 1 and r =1 then "p r"
when p = 1 and s =1 then "p s"
when r = 1 then r
when q = 1 then q
when r = 1 then r
when s = 1 then s
else ''
end

Answer 1

One solution could be this which uses a case for each attribute to return the correct value, surrounded by a trim to remove the trailing space.
with tbl(id, p, q, r, s) as (
select 5,1,0,0,1 from dual union all
select 14,0,0,0,1 from dual
)
select id,
trim(regexp_replace(case p when 1 then 'p' end ||
case q when 1 then 'q' end ||
case r when 1 then 'r' end ||
case s when 1 then 's' end, '(.)', '\1 '))
from tbl;
The real solution would be to fix the database design. This design technically violates Boyce-Codd 4th normal form in that it contains more than 1 independent attribute. The fact an ID "has" or "is part of" attribute p or q, etc should be split out. This design should be 3 tables, the main table with the ID, the lookup table containing info about attributes that the main ID could have (p, q, r or s) and the associative table that joins the two where appropriate (assuming an ID row could have more than one attribute and an attribute could belong to more than one ID), which is how to model a many-to-many relationship.
main_tbl main_attr attribute_lookup
ID col1 col2 main_id attr_id attr_id attr_desc
5 5 1 1 p
14 5 4 2 q
14 4 3 r
4 s
Then it would be simple to query this model to build your list, easy to maintain if an attribute description changes (only 1 place to change it), etc.
Select from it like this:
select m.ID, m.col1, listagg(al.attr_desc, ' ') within group (order by al.attr_desc) as attr_desc
from main_tbl m
join main_attr ma
on m.ID = ma.main_id
join attribute_lookup al
on ma.attr_id = al.attr_id
group by m.id, m.col1;

Answer 2

You can use concatenations with decode() functions
select id, decode(p,1,'p','')||decode(q,1,'q','')
||decode(r,1,'r','')||decode(s,1,'s','') as "String"
from t;
Demo
If you need spaces between letters, consider using :
with t(id,p,q,r,s) as
(
select 5,1,0,0,1 from dual union all
select 14,0,0,0,1 from dual union all
select 31,null,0,null,1 from dual union all
select 33,1,0,1,1 from dual
), t2 as
(
select id, decode(p,1,'p','')||decode(q,1,'q','')
||decode(r,1,'r','')||decode(s,1,'s','') as str
from t
), t3 as
(
select id, substr(str,level,1) as str, level as lvl
from t2
connect by level <= length(str)
and prior id = id
and prior sys_guid() is not null
)
select id, listagg(str,' ') within group (order by lvl) as "String"
from t3
group by id;
Demo

Answer 3

in my opinion, its a bad practice to use columns for relationships.
you should have two tables, one that's called arts and another that is called mapping art looks like this:
ID - ART
1 - p
2 - q
3 - r
4 - 2
...
and mapping maps your base-'ID's to your art-ids and looks like this
MYID - ARTID
5 - 1
5 - 4
afterwards, you should make use of oracles pivot operator. its more dynamically