fix calculate onchanged answers in ques stats

dal/db_query/queries.sql

@@ -544,22 +544,44 @@ WITH Funnel AS (
     HAVING
         COUNT(*) >= 1
     ),
+     LastContent AS (
+         SELECT
+             a.question_id,
+             a.content AS last_answer_content
+         FROM
+             answer a
+                 JOIN (
+                 SELECT
+                     session,
+                     question_id,
+                     MAX(created_at) AS last_created_at
+                 FROM
+                     answer
+                 WHERE
+                     quiz_id = $1
+                   AND created_at >= TO_TIMESTAMP($2)
+                   AND created_at <= TO_TIMESTAMP($3)
+                 GROUP BY
+                    question_id, session
+             ) AS last_created_at_one_session ON a.session = last_created_at_one_session.session AND a.question_id = last_created_at_one_session.question_id AND a.created_at = last_created_at_one_session.last_created_at
+     ),
      Questions AS (
         SELECT
             q.title AS question_title,
-            a.content AS answer_content,
+            lc.last_answer_content AS answer_content,
             CAST(
                 COUNT(CASE WHEN a.result = FALSE THEN 1 END) * 100.0 / NULLIF(SUM(COUNT(CASE WHEN a.result = FALSE THEN 1 END)) OVER (PARTITION BY q.id), 0) AS FLOAT8
             ) AS percentage
         FROM
             question q
+        JOIN LastContent lc ON q.id = lc.question_id
         JOIN answer a ON q.id = a.question_id
         WHERE
             a.quiz_id = $1
             AND a.created_at >= TO_TIMESTAMP($2)
             AND a.created_at <= TO_TIMESTAMP($3)
         GROUP BY
-            q.id, q.title, a.content
+            q.id, q.title, lc.last_answer_content
         HAVING
             COUNT(*) >= 1
 )