diff --git a/exchange-seats b/exchange-seats
new file mode 100644
index 0000000..70ac808
--- /dev/null
+++ b/exchange-seats
@@ -0,0 +1,9 @@
+select  
+case  
+when mod(id,2) =0 then id-1  
+when mod(id,2) !=0 and id=cnt then id 
+else id+1 
+end as id, 
+student 
+from seat ,(select max(id) as cnt from seat) s 
+order by id ;
diff --git a/rank-scores b/rank-scores
new file mode 100644
index 0000000..671bfe5
--- /dev/null
+++ b/rank-scores
@@ -0,0 +1 @@
+Select score,dense_rank() over(order by score desc) as rnk from scores;  
diff --git a/top-three-salaries b/top-three-salaries
new file mode 100644
index 0000000..4da9da2
--- /dev/null
+++ b/top-three-salaries
@@ -0,0 +1,7 @@
+with cte as ( 
+select e.name,e.salary,e.departmentid,d.name as department,dense_rank() over(partition by e.departmentid order by e.salary desc) rnk 
+from employee e  
+join  
+department d 
+on e.departmentid = d.id) 
+select department,name as employee,salary from cte where rnk <=3; 
diff --git a/tree-node b/tree-node
new file mode 100644
index 0000000..b0be1ea
--- /dev/null
+++ b/tree-node
@@ -0,0 +1,9 @@
+select id, 
+case  
+when p_id is null then 'Root' 
+when id not in (select distinct p_id from tree where p_id is not null) then 'Leaf' 
+else 'Inner' 
+END as type  
+from tree order by id; 
+
+