diff --git a/1.sql b/1.sql
new file mode 100644
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--- /dev/null
+++ b/1.sql
@@ -0,0 +1,28 @@
+# Write your MySQL query statement below
+WITH cte AS (
+    SELECT 
+        fail_date AS dt, 
+        'failed' AS period_state, 
+        RANK() OVER (ORDER BY fail_date) AS rnk
+    FROM Failed
+    WHERE YEAR(fail_date) = 2019
+
+    UNION ALL
+
+    SELECT 
+        success_date AS dt, 
+        'succeeded' AS period_state, 
+        RANK() OVER (ORDER BY success_date) AS rnk
+    FROM Succeeded
+    WHERE YEAR(success_date) = 2019
+),
+cte2 AS (
+    SELECT 
+        *, 
+        (RANK() OVER (ORDER BY dt) - rnk) AS group_rank
+    FROM cte
+)
+SELECT period_state, min(dt) as start_date,max(dt) as end_date
+FROM cte2
+group by group_rank, period_state
+order by 2;
diff --git a/2.sql b/2.sql
new file mode 100644
index 0000000..117b262
--- /dev/null
+++ b/2.sql
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+# Write your MySQL query statement belows
+with cte1 as(
+select name as America, row_number()over(order by name) as rnk
+from Student 
+where continent = 'America' 
+),
+cte2 as(
+    select name as Asia, row_number()over(order by name) as rnk
+from Student 
+where continent = 'Asia' 
+),
+cte3 as 
+(
+select name as Europe, row_number()over(order by name) as rnk
+from Student 
+where continent = 'Europe' )
+
+select cte1.America, cte2.Asia,cte3.Europe
+from cte2
+right join cte1
+on cte2.rnk=cte1.rnk
+left join cte3 
+on cte1.rnk=cte3.rnk
\ No newline at end of file
diff --git a/3.sql b/3.sql
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index 0000000..0ccfb8a
--- /dev/null
+++ b/3.sql
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+WITH cte1 AS (
+    SELECT 
+        e.department_id, 
+        AVG(s.amount) AS department_avg, 
+        DATE_FORMAT(s.pay_date, '%Y-%m') AS pay_month 
+    FROM 
+        salary s
+    JOIN 
+        employee e ON s.employee_id = e.employee_id 
+    GROUP BY 
+        e.department_id, 
+        pay_month
+),
+cte2 AS (
+    SELECT 
+        AVG(s.amount) AS company_avg, 
+        DATE_FORMAT(s.pay_date, '%Y-%m') AS pay_month 
+    FROM 
+        salary s
+    GROUP BY 
+        pay_month
+)
+SELECT 
+    cte1.pay_month, 
+    cte1.department_id, 
+    CASE 
+        WHEN cte1.department_avg > cte2.company_avg THEN 'higher' 
+        WHEN cte1.department_avg < cte2.company_avg THEN 'lower' 
+        ELSE 'same' 
+    END AS comparison
+FROM 
+    cte1
+JOIN 
+    cte2 ON cte1.pay_month = cte2.pay_month;
\ No newline at end of file
diff --git a/4.sql b/4.sql
new file mode 100644
index 0000000..5f776c2
--- /dev/null
+++ b/4.sql
@@ -0,0 +1,4 @@
+select player_id, min(event_date) as first_login
+from Activity
+group by player_id
+order by player_id
\ No newline at end of file