diff --git a/src/Database/Esqueleto/Utils.hs b/src/Database/Esqueleto/Utils.hs
index 236463675..2d823de2b 100644
--- a/src/Database/Esqueleto/Utils.hs
+++ b/src/Database/Esqueleto/Utils.hs
@@ -430,6 +430,7 @@ bool onFalse onTrue val = E.case_
   (E.else_ onFalse)
 
 -- called see greatest and least within postgresql
+-- TODO: this is buggy! Both return always the first argument if any argument is NULL!
 max, min :: PersistField a
          => E.SqlExpr (E.Value a)
          -> E.SqlExpr (E.Value a)
@@ -437,7 +438,7 @@ max, min :: PersistField a
 max a b = bool a b $ b E.>. a
 min a b = bool a b $ b E.<. a
 
--- these alternatives for max/min ought to be more efficient
+-- these alternatives for max/min ought to be more efficient; note that NULL is avoided by greatest/least
 greatest :: PersistField a => E.SqlExpr (E.Value a) -> E.SqlExpr (E.Value a) -> E.SqlExpr (E.Value a)
 greatest a b = E.unsafeSqlFunction "GREATEST" $ E.toArgList (a,b)
 
diff --git a/src/Handler/Utils/Users.hs b/src/Handler/Utils/Users.hs
index 0fe21a898..c94dda85b 100644
--- a/src/Handler/Utils/Users.hs
+++ b/src/Handler/Utils/Users.hs
@@ -273,6 +273,7 @@ data UserAssimilateExceptionReason
   | UserAssimilatePersonalisedSheetFileDifferentContent (Entity PersonalisedSheetFile) (Entity PersonalisedSheetFile)
   | UserAssimilateTutorialParticipantCollidingRegGroups (Entity TutorialParticipant) (Entity TutorialParticipant)
   | UserAssimilateCouldNotDetermineUserIdents
+  | UserAssimilateConflictingLmsQualifications (Set.Set QualificationId)
   deriving (Eq, Ord, Show, Generic, Typeable)
 
 assimilateUser :: UserId -- ^ @newUserId@
@@ -846,7 +847,21 @@ assimilateUser newUserId oldUserId = mapReaderT execWriterT $ do
             delete oldSFId
    in runConduit $ getStudyFeatures .| C.mapM_ upsertStudyFeatures
 
-  -- lms     
+  -- Qualifications and ongoing LMS   
+  -- LmsUser: insertSelectWithConflict impossible due to 2 simultaneous uniqueness constraints; UniqueLmsIdent requires proper update, prohibits insert and then delete
+  -- updateWhere [ LmsUserUser ==. oldUserId ] [ LmsUserUser =. newUserId ] -- might fail due to UniqueLmsQualficationUuser    
+  oldLms <- selectList [ LmsUserUser ==. oldUserId ] [ Asc LmsUserQualification ]
+  newLms <- selectList [ LmsUserUser ==. newUserId ] [ Asc LmsUserQualification ]
+  let projQ = lmsUserQualification . entityVal
+      oldQs = Set.fromList (projQ <$> oldLms)
+      newQs = Set.fromList (projQ <$> newLms)
+      qConflicts  = oldQs `Set.intersection` newQs
+      qResolvable = Set.fromList [ lmsUserQualification | Entity _ LmsUser{..} <- oldLms, isJust lmsUserEnded, lmsUserQualification `Set.member` qConflicts ] 
+      qProblems   = qConflicts `Set.difference` qResolvable 
+  unless (Set.null qProblems)   $ tellError $ UserAssimilateConflictingLmsQualifications qProblems
+  unless (Set.null qResolvable) $ deleteWhere [ LmsUserUser ==. oldUserId, LmsUserQualification <-. Set.toList qResolvable ] -- delete conflicting and finished LMS, which are still within auditDuration  
+  updateWhere [ LmsUserUser ==. oldUserId ] [ LmsUserUser =. newUserId ]
+  updateWhere [ QualificationEditUser ==. oldUserId ] [ QualificationEditUser =. newUserId ]
   E.insertSelectWithConflict
     UniqueQualificationUser
     (E.from $ \qualificationUser -> do
@@ -860,15 +875,52 @@ assimilateUser newUserId oldUserId = mapReaderT execWriterT $ do
           E.<&> (qualificationUser E.^. QualificationUserBlockedDue)
     )
     (\current excluded ->       
-      [ QualificationUserValidUntil  E.=. combineWith current excluded E.max QualificationUserValidUntil
-      , QualificationUserLastRefresh E.=. combineWith current excluded E.max QualificationUserLastRefresh
-      , QualificationUserFirstHeld   E.=. combineWith current excluded E.min QualificationUserFirstHeld
-      , QualificationUserBlockedDue  E.=. combineWith current excluded E.max QualificationUserBlockedDue
+      [ QualificationUserValidUntil  E.=. combineWith current excluded E.greatest QualificationUserValidUntil
+      , QualificationUserLastRefresh E.=. combineWith current excluded E.greatest QualificationUserLastRefresh
+      , QualificationUserFirstHeld   E.=. combineWith current excluded E.least    QualificationUserFirstHeld
+      , QualificationUserBlockedDue  E.=. combineWith current excluded E.greatest QualificationUserBlockedDue  -- Tested: PostgreSQL GREATEST/LEAST ignores NULL values
       ] 
     )
-  -- TODO: LmsUser!
   deleteWhere [ QualificationUserUser ==. oldUserId ]
 
+  -- Supervision is fully merged
+  E.insertSelectWithConflict
+    UniqueUserSupervisor
+    (E.from $ \userSupervisor -> do 
+      E.where_ $ userSupervisor E.^. UserSupervisorSupervisor E.==. E.val oldUserId
+      return $ UserSupervisor
+        E.<#  E.val newUserId
+        E.<&> (userSupervisor E.^. UserSupervisorUser)
+        E.<&> (userSupervisor E.^. UserSupervisorRerouteNotifications)
+    )
+    (\current excluded -> [ UserSupervisorRerouteNotifications E.=. (current E.^. UserSupervisorRerouteNotifications E.||. excluded E.^. UserSupervisorRerouteNotifications)  ] )
+  deleteWhere [ UserSupervisorSupervisor ==. oldUserId]    
+
+  E.insertSelectWithConflict
+    UniqueUserSupervisor
+    (E.from $ \userSupervisor -> do 
+      E.where_ $ userSupervisor E.^. UserSupervisorUser E.==. E.val oldUserId
+      return $ UserSupervisor
+        E.<#  (userSupervisor E.^. UserSupervisorSupervisor)
+        E.<&> E.val newUserId
+        E.<&> (userSupervisor E.^. UserSupervisorRerouteNotifications)
+    )
+    (\current excluded -> [ UserSupervisorRerouteNotifications E.=. (current E.^. UserSupervisorRerouteNotifications E.||. excluded E.^. UserSupervisorRerouteNotifications)  ] )
+  deleteWhere [ UserSupervisorUser ==. oldUserId]    
+
+  -- Companies, in conflict, keep the newUser-Company as is
+  E.insertSelectWithConflict
+    UniqueCompanyUser
+    (E.from $ \userCompany -> do 
+      E.where_ $ userCompany E.^. UserCompanyUser E.==. E.val oldUserId
+      return $ UserCompany 
+        E.<#  (userCompany E.^. UserCompanyCompany)
+        E.<&> E.val newUserId
+        E.<&> (userCompany E.^. UserCompanySupervisor)
+    )
+    (\current _excluded -> [ UserCompanySupervisor E.=. (current E.^. UserCompanySupervisor)] )
+  deleteWhere [ UserCompanyUser ==. oldUserId]
+
   userIdents <- E.select . E.from $ \user -> do
     E.where_ $ user E.^. UserId `E.in_` E.valList [newUserId, oldUserId]
     return ( user E.^. UserId