Completed Sql1

problem1.sql

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+-- Write your PostgreSQL query statement below
+SELECT name, population, area
+FROM World
+WHERE area >= 3000000
+OR population >= 25000000;

problem2.sql

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+CREATE OR REPLACE FUNCTION NthHighestSalary(N INT) RETURNS TABLE (Salary INT) AS $$
+BEGIN
+  RETURN QUERY (
+    -- Write your PostgreSQL query statement below.
+    WITH CTE AS (
+        SELECT e.salary, DENSE_RANK() OVER(ORDER BY e.salary DESC) AS rnk
+        FROM Employee e
+    )
+    SELECT DISTINCT c.salary
+    FROM CTE c
+    WHERE c.rnk = N
+  );
+END;
+$$ LANGUAGE plpgsql;

problem3.sql

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+-- Write your PostgreSQL query statement below
+DELETE FROM Person
+USING Person p2
+WHERE Person.email = p2.email
+AND Person.id > p2.id;