feat(sql-2): solved problem 1 and problem 2

problem1-178-rank-scores.sql

@@ -0,0 +1,5 @@
+select
+score,
+dense_rank() over(order by score desc) AS `rank`
+from
+Scores

problem2-626-exchange-seats.sql

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+--case statement
+select
+     case
+        when id%2=1 and id < (select max(id) from seat) then id + 1
+        when id%2=0 then id-1
+     else
+        id
+    END AS id,
+    student
+from
+    seat
+order by id
+
+--self join
+SELECT
+  s1.id,
+  COALESCE(s2.student, s1.student) AS student
+FROM Seat s1
+LEFT JOIN Seat s2
+  ON (
+    (s1.id % 2 = 1 AND s2.id = s1.id + 1) OR
+    (s1.id % 2 = 0 AND s2.id = s1.id - 1)
+  )
+ORDER BY s1.id;
+
+--window function lead,lag
+SELECT
+  id,
+  case
+     when id%2=1 and id < (select max(id) from seat) then lead(student) over(order by id)
+     when id%2=0 then lag(student) over(order by id)
+     else student
+   END as student
+FROM Seat
+ORDER BY id
+
+--bitwise operator
+SELECT
+  s1.id,
+  coalesce(s2.student,s1.student) as student
+FROM Seat s1
+left join Seat s2
+on (s1.id +1)^1-1=s2.id
+ORDER BY id

problem3-608-tree-nodes.sql

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+--case statement
+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;
+
+--if condition
+SELECT
+    id,
+    IF(P_id is null,'Root',IF(id not in (select distinct p_id from Tree where p_id is not null),'Leaf','Inner')) AS type
+FROM Tree;
+
+--union
+
+SELECT
+    id,
+    'Root' AS type
+FROM Tree
+where p_id is null
+
+union
+
+SELECT
+    id,
+    'Leaf' AS type
+FROM Tree
+where id not in (select distinct p_id from Tree where p_id is not null) and p_id is not null
+
+union
+
+SELECT
+    id,
+    'Inner' AS type
+FROM Tree
+where id in (select distinct p_id from Tree) and p_id is not null