Was testing a bit Moodle 1.9 under Oracle, when I got this error:

ORA-00932: inconsistent datatypes: expected CLOB got CHAR

SELECT r.id, COALESCE(rn.text, r.name) AS name FROM m_role r JOIN ( SELECT DISTINCT allowassign as allowedrole FROM m_role_allow_assign raa WHERE raa.roleid IN (3,1) ) ar ON r.id=ar.allowedrole JOIN m_role_capabilities rc ON (r.id = rc.roleid AND rc.capability = 'moodle/course:view' AND rc.capability != 'moodle/site:doanything') LEFT OUTER JOIN m_role_names rn ON (rn.roleid = r.id AND rn.contextid = 23) ORDER BY sortorder ASC

It seems that the role_names->text field is of type TEXT (CLOB) and that prevents it to be used within COALESCE and other functions.

If I'm not wrong that table, role_names, is exclusively used to name roles in a different way per context. If that is the only usage I would recommend to:

1) create one new role_names->name char(255) not null field.
2) copy current role_names->text contents to role_names->name
3) drop role_names->text
4) Change usages from the old field to the new one.

That way the field will be better and his behaviour cross-db.

Ciao

P.S.: Raising this to critical... to alarm about it (prevents Oracle usage completely)