Index: lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/dbupdates/patch20200218.sql
===================================================================
diff -u
--- lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/dbupdates/patch20200218.sql	(revision 0)
+++ lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/dbupdates/patch20200218.sql	(revision 0a5a11351daa8e308190921254096c712ce88837)
@@ -0,0 +1,21 @@
+-- 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-4976 Introduce an extra column which holds the same information as parent table, then add unique index to prevent duplicates
+
+ALTER TABLE tl_lamc11_usr_attempt ADD COLUMN qb_tool_question_uid BIGINT AFTER uid;
+
+UPDATE tl_lamc11_usr_attempt AS a JOIN lams_qb_tool_answer AS q ON a.uid = q.answer_uid
+SET a.qb_tool_question_uid = q.tool_question_uid;
+
+ALTER TABLE tl_lamc11_usr_attempt MODIFY COLUMN qb_tool_question_uid BIGINT NOT NULL,
+								  ADD UNIQUE INDEX IDX_attempt_duplicate_prevent (qb_tool_question_uid, que_usr_id);
+
+-- 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;
Index: lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/model/McUsrAttempt.java
===================================================================
diff -u -rf49dd9f6b076828f464fc954bb9c3dc0c87e8b37 -r0a5a11351daa8e308190921254096c712ce88837
--- lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/model/McUsrAttempt.java	(.../McUsrAttempt.java)	(revision f49dd9f6b076828f464fc954bb9c3dc0c87e8b37)
+++ lams_tool_lamc/src/java/org/lamsfoundation/lams/tool/mc/model/McUsrAttempt.java	(.../McUsrAttempt.java)	(revision 0a5a11351daa8e308190921254096c712ce88837)
@@ -66,6 +66,11 @@
     @Column
     private boolean passed;
 
+    // this is a copy of tool_question_uid from lams_qb_tool_answer, so we can create an unique index on it and que_usr_id
+    // there are no getters or setter for this column as they are not needed
+    @Column(name = "qb_tool_question_uid")
+    private Long qbToolQuestionUid;
+
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "que_usr_id")
     private McQueUsr mcQueUsr;
@@ -79,7 +84,7 @@
     public McUsrAttempt(Date attemptTime, McQueContent mcQueContent, McQueUsr mcQueUsr, QbOption qbOption, Integer mark,
 	    boolean passed, boolean attemptCorrect, int confidenceLevel) {
 	this.attemptTime = attemptTime;
-	this.qbToolQuestion = mcQueContent;
+	setMcQueContent(mcQueContent);
 	this.mcQueUsr = mcQueUsr;
 	this.qbOption = qbOption;
 	this.mark = mark;
@@ -105,6 +110,7 @@
 
     public void setMcQueContent(McQueContent mcQueContent) {
 	this.qbToolQuestion = mcQueContent;
+	this.qbToolQuestionUid = this.qbToolQuestion.getUid();
     }
 
     public McQueUsr getMcQueUsr() {
@@ -160,6 +166,10 @@
 	this.confidenceLevel = confidenceLevel;
     }
 
+    public Long getQbToolQuestionUid() {
+	return qbToolQuestionUid;
+    }
+
     /**
      * Get the mark for displaying to the user. If retries or passmark is off, then just check whether or not answer is
      * correct If retries and passmark is on, then we only want the marks if the user has passed!