Uhm, that GROUP clause it 100% wrong, I guess it only works under some DBs because it's used as "1" (column position).

AFAIK, then only cross-db way to do that is to replicate the complete CASE... expression in the GROUP BY clause. Nor column positions nor aliases are cross-db (only MySQL and PostgreSQL support them).

Going to work on some test & solution...

Confirmed, only the "complete expression in GROUP BY" alternative is correct and cross-db here. Fix and test added (test passing against the RDBMS).

+1 from me. Good fix.

Strange that GROUP BY boolean does not work. However, for this query it does not matter, because we want to group by the case, and the group by and the select fields have to match.

Thanks Eloy, this has been integrated now

unit tests are ok

testing quiz->statistics->first attempt+show report = ok,
when testing for recalculation and quiz->statistics -> all attempts (& recalculation) :

Debug info: ORA-01008: not all variables bound
INSERT INTO m_quiz_question_statistics (slot,s,subquestion,subquestions,randomguessscore,questionid,positions,maxmark,facility,sd,discriminationindex,discriminativeefficiency,negcovar,effectiveweight,quizstatisticsid) VALUES (:o_slot,:s,:o_subquestion,:o_subquestions,:o_randomguessscore,:o_questionid,:o_positions,:o_maxmark,:o_facility,:o_sd,:o_discriminationindex,:o_discriminativeefficiency,:o_negcovar,:o_effectiveweight,:o_quizstatisticsid)
[array (
'o_slot' => 1,
'o_s' => 2,
'o_subquestion' => 0,
'o_subquestions' => '',
'o_randomguessscore' => 0.5,
'o_questionid' => '3',
'o_positions' => 1,
'o_maxmark' => '1',
'o_facility' => 1,
'o_sd' => 0,
'o_discriminationindex' => NULL,
'o_discriminativeefficiency' => NULL,
'o_negcovar' => 0,
'o_effectiveweight' => 0,
'o_quizstatisticsid' => 1,
)]
Stack trace:
line 397 of \lib\dml\moodle_database.php: dml_write_exception thrown
line 268 of \lib\dml\oci_native_moodle_database.php: call to moodle_database->query_end()
line 1176 of \lib\dml\oci_native_moodle_database.php: call to oci_native_moodle_database->query_end()
line 1219 of \lib\dml\oci_native_moodle_database.php: call to oci_native_moodle_database->insert_record_raw()
line 846 of \mod\quiz\report\statistics\report.php: call to oci_native_moodle_database->insert_record()
line 889 of \mod\quiz\report\statistics\report.php: call to quiz_statistics_report->cache_stats()
line 140 of \mod\quiz\report\statistics\report.php: call to quiz_statistics_report->get_quiz_and_questions_stats()
line 100 of \mod\quiz\report.php: call to quiz_statistics_report->display()

please feel free to pass if its a different code area from the patch.

Great, "s" being converted to ":s" and "o_s" placeholder.

I'm passing this because it's related with the mess created by MDL-26842 and being fixed by MDL-28080.

Ciao

Pass, thanks!

git & cvs repositories have been populated with this solution. Many thanks for your collaboration, yay!

Closing, ciao