datalib: get_logs_user*() - fix invalid SQL - MDL-12426

Oracle does not accept column labels in the GROUP BY section -
get_logs_usercourse() and get_logs_userday() were computing the
day/hours column and using it in the GROUP BY. The compatible fix
is to reproduce the same computation in the GROUP BY section.

Credit for the fix goes to Dennis Rochford <[email protected]>.

lib/datalib.php

@@ -1941,7 +1941,7 @@ function get_logs_usercourse($userid, $courseid, $coursestart) {
                             FROM {$CFG->prefix}log
                            WHERE userid = '$userid'
                              AND time > '$coursestart' $courseselect
-                        GROUP BY day ");
+                        GROUP BY floor((time - $coursestart)/". DAYSECS .") ");
 }
 
 /**
@@ -1968,7 +1968,7 @@ function get_logs_userday($userid, $courseid, $daystart) {
                             FROM {$CFG->prefix}log
                            WHERE userid = '$userid'
                              AND time > '$daystart' $courseselect
-                        GROUP BY hour ");
+                        GROUP BY floor((time - $daystart)/". HOURSECS .") ");
 }
 
 /**