Index: lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/dbupdates/patch20171011.sql
===================================================================
diff -u
--- lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/dbupdates/patch20171011.sql	(revision 0)
+++ lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/dbupdates/patch20171011.sql	(revision ba995699c252120c1dfcbf13e0043993a804abe6)
@@ -0,0 +1,31 @@
+-- Turn off autocommit, so nothing is committed if there is an error
+SET AUTOCOMMIT = 0;
+SET FOREIGN_KEY_CHECKS=0;
+----------------------Put all sql statements below here-------------------------
+
+-- LDEV-4438 Add unique constraint to prevent duplicate results with 'latest' flag being ON
+
+--remove all duplicates that have identical pairs (assessment_uid, user_uid, latest) where latest=1 
+DELETE a
+FROM tl_laasse10_assessment_result as a, tl_laasse10_assessment_result as b
+WHERE
+          (a.assessment_uid   = b.assessment_uid OR a.assessment_uid IS NULL AND b.assessment_uid IS NULL)
+      AND (a.user_uid = b.user_uid OR a.user_uid IS NULL AND b.user_uid IS NULL)
+      AND (a.latest = b.latest AND latest = 1)
+      AND a.uid < b.uid;
+      
+--set up tl_laasse10_assessment_result table to properly handle constraint
+UPDATE tl_laasse10_assessment_result SET latest=NULL WHERE latest='0';
+ALTER TABLE tl_laasse10_assessment_result CHANGE COLUMN latest latest TINYINT(1) NULL DEFAULT NULL;
+
+--add unique constraint
+ALTER TABLE tl_laasse10_assessment_result ADD UNIQUE KEY UQ_tl_laasse10_assessment_result_5 (assessment_uid, user_uid, latest);
+
+UPDATE lams_tool SET tool_version='20171011' WHERE tool_signature='laasse10';
+
+----------------------Put all sql statements above here-------------------------
+
+-- If there were no errors, commit and restore autocommit to on
+COMMIT;
+SET AUTOCOMMIT = 1;
+SET FOREIGN_KEY_CHECKS=1;
\ No newline at end of file
Index: lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/model/AssessmentResult.java
===================================================================
diff -u -re10da332d88104fe61b1f646b8bcac22bbfd15f0 -rba995699c252120c1dfcbf13e0043993a804abe6
--- lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/model/AssessmentResult.java	(.../AssessmentResult.java)	(revision e10da332d88104fe61b1f646b8bcac22bbfd15f0)
+++ lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/model/AssessmentResult.java	(.../AssessmentResult.java)	(revision ba995699c252120c1dfcbf13e0043993a804abe6)
@@ -42,7 +42,7 @@
     //date when user has started activity (pressed start button) that has time limitation
     private Date timeLimitLaunchedDate;
     //indicates the latest retry
-    private boolean isLatest;
+    private Boolean isLatest;
     private Date finishDate;
     private AssessmentUser user;
     private Long sessionId;
@@ -122,11 +122,11 @@
      *
      * @return
      */
-    public boolean isLatest() {
+    public Boolean isLatest() {
 	return isLatest;
     }
 
-    public void setLatest(boolean isLatest) {
+    public void setLatest(Boolean isLatest) {
 	this.isLatest = isLatest;
     }
 
Index: lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/service/AssessmentServiceImpl.java
===================================================================
diff -u -r60d9a173d5590295376322fc3e857ae2dca37717 -rba995699c252120c1dfcbf13e0043993a804abe6
--- lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/service/AssessmentServiceImpl.java	(.../AssessmentServiceImpl.java)	(revision 60d9a173d5590295376322fc3e857ae2dca37717)
+++ lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/service/AssessmentServiceImpl.java	(.../AssessmentServiceImpl.java)	(revision ba995699c252120c1dfcbf13e0043993a804abe6)
@@ -469,8 +469,9 @@
 
 	    // mark previous attempt as being not the latest any longer
 	    } else {
-		lastResult.setLatest(false);
+		lastResult.setLatest(null);
 		assessmentResultDao.saveObject(lastResult);
+		assessmentResultDao.flush();
 	    }
 	}