sql 6

1.sql

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+
+WITH cte AS (
+    SELECT 
+        player_id AS p, 
+        MIN(event_date) AS e
+    FROM Activity
+    GROUP BY player_id
+)
+SELECT a.player_id, a.device_id
+FROM Activity a
+JOIN cte 
+ON a.player_id = cte.p AND a.event_date = cte.e;

2.sql

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+SELECT 
+    player_id, event_date ,
+    SUM(games_played) OVER (PARTITION BY player_id order by event_date) AS games_played_so_far
+FROM Activity;

3.sql

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+select round(sqrt(min(pow(p1.x-p2.x,2)+pow(p1.y-p2.y,2))),2) as shortest
+from Point2D p1
+join Point2d p2
+where p1.x!=p2.x or p2.y!=p1.y

4.sql

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+select p.firstname,p.lastname, 
+a.city, a.state 
+from Person p
+left join Address a
+on p.personId=a.personId

5.sql

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+with cte as (select customer_id, YEAR(order_date) as yr, sum(price) as price
+from Orders
+group by customer_id,yr
+order by customer_id, yr
+)
+
+select c1.customer_id 
+from cte c1
+left join cte c2
+on  c1.customer_id =  c2.customer_id
+and c1.yr+1=c2.yr and c1.price<c2.price
+group by  c1.customer_id
+having count(*) - count( c2.customer_id) =1