APPLIES TO:
Oracle Database - Enterprise Edition - Version 11.2.0.4 to 11.2.0.4 [Release 11.2]
Oracle Database - Enterprise Edition - Version 12.1.0.2 to 12.1.0.2 [Release 12.1]
Workspace Manager - Version 9.2.0.1 to 11.2.0.2 [Release 9.2 to 11.2]
Oracle Spatial and Graph - Version 12.1.0.2 to 12.1.0.2 [Release 12.1]
Information in this document applies to any platform.
***Checked for relevance on 17-Dec-2012***
GOAL
This document is meant to assist both Customers and Oracle Support Analysts in handling situations and Service Requests in which the problem is related to the usage of the undocumented function WMSYS.WM_CONCAT.
SOLUTION
WMSYS.WM_CONCAT function is used internally and for this reason it is UN-documented.
Oracle Development uses internal procedure/functions like WMSYS.WM_CONCAT to support Oracle products.
Oracle suggests that customers do not use internal objects, procedures, data dictionary tables in their applications because they may be changed at any time.
If Oracle Development needs to change this function, to correct a bug or enhance performances, they make all the changes internally and the changes are NOT published.
Any non-Oracle document found on Internet referring to this function is not reliable. Anything Oracle does support, is documented in our guides and/or published documents searchable on MyOracle Support.
It should be relatively straightforward for a developer to create an aggregate function similar to WMSYS.WM_CONCAT.
Some useful links that can be used to understand how to proceed are:
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:2196162600402
http://www.oracle-base.com/articles/10g/StringAggregationTechniques.php
http://rwijk.blogspot.com/2008/05/string-aggregation-with-model-clause.html
Additionally, from 11.2 release onwards it might be a good idea that of using for this same purpose the analytics function named LISTAGG.
You can find a reference ans some good example inthe following documentation:
Oracle® Database SQL Language Reference 11g Release 2 (11.2)
Oracle® Database SQL Language Reference 12c Release 1 (12.1)