Oracle is case sensitive, so a query like:
select * from mdl_user where firstname = "name"

will only return exact matches - it won't return "Name", "NAME" etc like Mysql/postgres do.

this is a problem in many areas of moodle code and there seem to be various bugs in the tracker that are related.

Oracle 10g allows the setting of a Session var that changes this.

one of our clients came up with this code which they've put in lib/setup.lib which seems to fix it nicely!

if($CFG->dbtype == 'oci8po'){
if (!empty ($CFG->nls_sort))

{ $db->execute('ALTER SESSION SET NLS_SORT=' . $CFG->nls_sort); }

if (!empty ($CFG->nls_comp))

{ $db->execute('ALTER SESSION SET NLS_COMP=' . $CFG->nls_comp); }

}

they have then placed the correct vars for their version of oracle in the config vars $CFG->nls_sort and $CFG-nls_comp.

I think we should be a bit more clever and determine which Oracle version they are using, and if they are using a version prior to 10gR2 then use "ANSI" as the NLS_COMP and 'BINARY_CI' for NLS_SORT
but if they're using 10gR2 or higher use 'LINGUISTIC' for NLS_COMP and 'BINARY_CI' for NLS_SORT

there's a good Oracle article here that describes the commands:
http://www.orafaq.com/node/91

NOTE: the changes for older versions of oracle will not make "LIKE" queries case insensitve - only oracle 10gR2 supports this with the above changes.

Dan