Concatenate rows into CLOB

Question

There are many similar questions on this subject, but I can't find any with solutions that keep into account anything with an end result too large for varchar2.

So what I'm trying to do is change this:

Column1 | Column2
-------- --------
1         Hello
1         world,
1         please help
2         Thanks
2         world,
2         you're the best.

Into this:

Column1 | Column2
-------- --------
1         Hello world, please help
2         Thanks world, you're the best.

My particular problem is that there are a few cases where the new concatenated value exceeds 4000 characters, so I can't use LISTAGG as I hoped to. I'm particularly interested in solutions without having to write a function, but either will do.

Answer 1

As de.hh.holger already pointed out, the LISTAGG WITH CLOB? STRING AGGREGATION EXCEEDING 4000 CHARACTERS WITH XMLAGG does indeed solve this issue.

I have elaborated a little further on the subject and this should do the trick in case of a really long string message:

SELECT
   table_row_id,
   DBMS_XMLGEN.CONVERT (
     EXTRACT(
       xmltype('<?xml version="1.0"?><document>' ||
               XMLAGG(
                 XMLTYPE('<V>' || DBMS_XMLGEN.CONVERT(data_value)|| '</V>')
                 order by myOrder).getclobval() || '</document>'),
               '/document/V/text()').getclobval(),1) AS data_value
FROM (
   SELECT 1 myOrder, 1 table_row_id,'abcdefg>' data_value FROM dual
   UNION ALL
   SELECT 2, 1 table_row_id,'hijklmn' data_value FROM dual
   UNION ALL
   SELECT 3, 1 table_row_id,'opqrst' data_value FROM dual
   UNION ALL
   SELECT 4, 1 table_row_id,'uvwxyz' data_value FROM dual)
GROUP BY
   table_row_id

Answer 2

SELECT Column1 , LISTAGG(Column2, ' ') 
WITHIN GROUP (ORDER BY Column2) AS employees
FROM   Table1
GROUP BY Column1 ;

Please have a look at this Article