Group By inside Rtrim(Xmlagg (Xmlelement (e,element || ',')).extract ( '//text()' ).GetClobVal(), ',') - oracle

Question

I need to group values ​​inside a query using (or not) the command Rtrim(Xmlagg (Xmlelement (e,column || ',')).extract ( '//text()' ).GetClobVal(), ','), but I can't find any literature where explain a way to group the data inside this command. The code is very simple, as you can see below:
SELECT ID,
Rtrim(Xmlagg (Xmlelement (and, CONTRACTS || ',')).extract ( '//text()' ).GetClobVal(), ',') AS CONTRACTS
FROM TABLE_A
GROUP BY ID
The result in CONTRACTS is always repeated when the ID is found, thats ok, it´s working!
ID
CONTRACTS
876
1,1,1,2,3,3
But what I really need is this return:
ID
CONTRACTS
876
1,2,3
It´s not necessary to use the command Rtrim(Xmlagg (Xmlelement (e,column || ',')).extract ( '//text()' ).GetClobVal(), ','), instead, I just use to concatenate element with comma "," in the same column.
If anyone can help me, I would be very grateful!

Answer 1

If your values will fit into a VARCHAR2 data type (rather than a CLOB) then you can use a nested sub-query to get the DISTINCT values for each ID:
SELECT ID,
LISTAGG(contracts, ',') WITHIN GROUP (ORDER BY contracts) AS CONTRACTS
FROM ( SELECT DISTINCT id, contracts FROM TABLE_A)
GROUP BY ID
Or, from Oracle 19c, it is built-in to LISTAGG:
SELECT ID,
LISTAGG(DISTINCT contracts, ',') WITHIN GROUP (ORDER BY contracts) AS CONTRACTS
FROM TABLE_A
GROUP BY ID
If you want a CLOB then you can use the same technique as the first query:
SELECT ID,
Rtrim(
Xmlagg(
Xmlelement(name, CONTRACTS || ',')
ORDER BY contracts
).extract ( '//text()' ).GetClobVal(),
','
) AS CONTRACTS
FROM (SELECT DISTINCT id, contracts FROM TABLE_A)
GROUP BY ID
Which, for the sample data:
CREATE TABLE table_a (id, contracts) AS
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 2 FROM DUAL UNION ALL
SELECT 876, 2 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL;
All output:
ID
CONTRACTS
876
1,2,3
db<>fiddle here

Answer 2

It's much easier to do all those operation in XML functions: DBFiddle
SELECT--+ NO_XML_QUERY_REWRITE
id,
xmlquery(
'string-join(distinct-values($R/R/X/text()),",")'
passing
Xmlelement(
R,
Xmlagg(
Xmlelement (X, CONTRACTS)
order by CONTRACTS
)) as R
RETURNING CONTENT
) AS CONTRACTS
FROM TABLE_A
GROUP BY ID;
Full example with test data:
with table_a (id, contracts) AS (
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 1 FROM DUAL UNION ALL
SELECT 876, 2 FROM DUAL UNION ALL
SELECT 876, 2 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL UNION ALL
SELECT 876, 3 FROM DUAL
)
SELECT--+ NO_XML_QUERY_REWRITE
id,
xmlquery(
'string-join(distinct-values($R/R/X/text()),",")'
passing
Xmlelement(
R,
Xmlagg(
Xmlelement (X, CONTRACTS)
order by CONTRACTS
)) as R
RETURNING CONTENT
) AS CONTRACTS
FROM TABLE_A
GROUP BY ID;