Pivot with dynamic columns in oracle 11g - sql

Question

I have 3 tables (Potions and Reagents and relation of both) and I want to pivot the results, pass to explain:
TABLE POTIONS
ID DESCRIPTION
1 Heal
2 Mana
3 Explosion
TABLE REAGENTS
ID DESCRIPTION
1 Base
2 Mandrake
3 Tulip
4 Sunflower
5 Powder
TABLE POTION_REAGENTS
ID_POTION ID_REAGENT
1 1
1 3
2 1
2 2
2 5
3 4
3 5
I want to obtain the result like this but I dont know how pivot with dynamic columns
POTION REAG_1 REAG_2 REAG_3
Heal Base Tulip NULL
Mana Base Mandrake Powder
Explosion Sunflower Powder NULL
I want if new potion have 4 Reagent the select return's REAG_4 column. Its possible?
Thx for your time!

Answer 1

You cannot use a dynamic pivot; you must have a pre-defined set of values in the PIVOT clause. However, you can use the ROW_NUMBER analytic function to pre-generate a numeric index for potion reagents:
SELECT potion,
reagent1,
reagent2,
reagent3,
reagent4
FROM (
SELECT p.id,
p.description AS potion,
r.description AS reagent,
ROW_NUMBER() OVER (PARTITION BY p.id ORDER BY r.description) AS rn
FROM potions p
INNER JOIN potion_reagents pr
ON (p.id = pr.id_potion)
INNER JOIN reagents r
ON (pr.id_reagent = r.id)
)
PIVOT (
MAX(reagent) FOR rn IN (1 AS reagent1, 2 AS reagent2, 3 AS reagent3, 4 AS reagent4)
)
Which, for your sample data:
CREATE TABLE POTIONS (ID, DESCRIPTION) AS
SELECT 1, 'Heal' FROM DUAL UNION ALL
SELECT 2, 'Mana' FROM DUAL UNION ALL
SELECT 3, 'Explosion' FROM DUAL;
CREATE TABLE REAGENTS (ID, DESCRIPTION) AS
SELECT 1, 'Base' FROM DUAL UNION ALL
SELECT 2, 'Mandrake' FROM DUAL UNION ALL
SELECT 3, 'Tulip' FROM DUAL UNION ALL
SELECT 4, 'Sunflower' FROM DUAL UNION ALL
SELECT 5, 'Powder' FROM DUAL;
CREATE TABLE POTION_REAGENTS (ID_POTION, ID_REAGENT) AS
SELECT 1, 1 FROM DUAL UNION ALL
SELECT 1, 3 FROM DUAL UNION ALL
SELECT 2, 1 FROM DUAL UNION ALL
SELECT 2, 2 FROM DUAL UNION ALL
SELECT 2, 5 FROM DUAL UNION ALL
SELECT 3, 4 FROM DUAL UNION ALL
SELECT 3, 5 FROM DUAL;
Outputs:
POTION
REAGENT1
REAGENT2
REAGENT3
REAGENT4
Explosion
Powder
Sunflower
null
null
Heal
Base
Tulip
null
null
Mana
Base
Mandrake
Powder
null
fiddle

Answer 2

To me it seems you're a making a game or something of a kind. That means there is another "external" programming is being used to process data you're getting from the database.
For that case there is a possibility to obtain a pivot result with dynamical set of columns in XML format. You need the "pivot xml"
select *
from (select p.description p_desc,
r.description r_desc,
'REAG_' || row_number() over (partition by p.description order by r.description) reag_num
from potion_reagents pr
join reagents r
on r.id = pr.id_reagent
join potions p
on p.id = pr.id_potion)
pivot xml(
min(r_desc)
for reag_num in (ANY)
)
As I said, the answer you'll get will be in XML format which is quite simple to parse. Here is an example for "Mana" potion with a fourth reagent I named "Secret"
<PivotSet>
<item>
<column name = "REAG_NUM">REAG_1</column>
<column name = "MIN(R_DESC)">Base</column>
</item>
<item>
<column name = "REAG_NUM">REAG_2</column>
<column name = "MIN(R_DESC)">Mandrake</column>
</item>
<item>
<column name = "REAG_NUM">REAG_3</column>
<column name = "MIN(R_DESC)">Powder</column>
</item>
<item>
<column name = "REAG_NUM">REAG_4</column>
<column name = "MIN(R_DESC)">Secret</column>
</item>
</PivotSet>
Here's a dbfiddle with an example based on data you've provide us with