commit

Game_play_analysis_i.sql

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+SELECT player_id, MIN(event_date) AS 'first_login'
+FROM Activity GROUP BY player_id;

avg_salary.sql

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+with temp as (
+            select s.pay_date, e.department_id,
+                   avg(s.amount) over(partition by s.pay_date order by s.pay_date) avg_company_salary,
+                   avg(s.amount) over(partition by e.department_id, s.pay_date order by s.pay_date) avg_dept_salary
+            from salary s
+            inner join employee e
+            on s.employee_id = e.employee_id
+            )
+select date_format(pay_date,"%Y-%m") as pay_month,
+       department_id, 
+       case when avg_dept_salary > avg_company_salary then 'higher'
+            when avg_dept_salary < avg_company_salary then 'lower'
+            else 'same' end as comparison
+from temp
+group by pay_month, department_id order by pay_date desc;

report_contiguous_dates.sql

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+with state_table as(
+  select fail_date dates, 'failed' state from Failed where year(fail_date) = 2019
+  union
+  select *, 'succeeded' state from Succeeded where year(success_date) = 2019
+),
+rank_table as(
+  select dates, state, dense_rank()over(partition by state order by dates,state) rnk from state_table
+)
+select state period_state, min(dates) start_date, min(dates)+ interval count(dates)-1 day end_date 
+from rank_table group by state,dates-interval rnk day order by start_date

student_report.sql

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+select America,Asia,Europe from (select name as America,row_number()over(order by name) as r1
+from student
+where continent='America') am
+left join (select name as Asia,row_number()over(order by name) as r1
+from student
+where continent='Asia') asi on am.r1=asi.r1 
+left join(select name as Europe,row_number()over(order by name) as r1
+from student
+where continent='Europe') e
+
+on am.r1=e.r1