Done SQL1

Problem1_Big Countries.sql

@@ -0,0 +1,4 @@
+select name,population,area
+from world
+where area >= 3000000
+or population >= 25000000

Problem2_NthHighestSalary.sql

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+CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
+BEGIN
+  RETURN (
+    with cte as( 
+      select id,salary,dense_rank() over (order by salary desc) as salaryrank from employee
+    )
+    select distinct ifnull(salary,null) as getNthHighestSalary
+    from cte where salaryrank=N
+  );
+END

Problem3_DeleteDuplicateEmails.sql

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+delete p1 
+from person p1 cross join person p2
+where p1.email=p2.email and p1.id>p2.id