Added five solutions/SQL6

problem1.sql

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+-- # Write your MySQL query statement below
+with cte as(
+select player_id,
+device_id,
+rank()over(partition by player_id order by event_date) as 'rnk'
+from activity)
+
+select player_id,device_id
+from cte
+where rnk=1;

problem2.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;

problem3.sql

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+
+with cte as(
+select *, row_number()over()as row_num
+from Point2D)
+
+select round(min(sqrt(pow((c.x-p.x),2)+pow((c.y-p.y),2))),2) as shortest
+from cte c
+inner join cte p
+on c.row_num<p.row_num;
+

problem4.sql

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+# Write your MySQL query statement below
+select p.firstname,p.lastname,a.city,a.state
+from person p
+left join address a on p.personID=a.personID;

problem5.sql

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