solve: Hard faizanxmulla#11, faizanxmulla#13

Author: faizanxmulla

interview-query-solutions/Hard/11-sequentially-fill-in-integers.sql

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+-- Solution 1: using recursive cte
+
+WITH RECURSIVE CTE as (
+    SELECT int_numbers, 1 as flag
+    FROM   tbl_numbers
+    UNION ALL
+    SELECT int_numbers, flag+1
+    FROM   CTE
+    WHERE  flag < int_numbers
+)
+SELECT   int_numbers as seq_numbers
+FROM     CTE
+ORDER BY 1
+
+
+
+-- Solution 2: very easy in PostgreSQL
+-- using CROSS join & generate_series
+
+SELECT int_numbers AS seq_numbers 
+FROM   tbl_numbers CROSS JOIN generate_series(1, int_numbers)
+
+
+-- NOTE: read the question and immendiately thought of recursive cte.

interview-query-solutions/Hard/13-johns-new-best-friend.sql

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+WITH already_friends AS (
+    SELECT friend_id 
+    FROM   friends 
+    WHERE  user_id=3
+),
+blocked AS (
+    SELECT blocked_id 
+    FROM   blocks 
+    WHERE  user_id=3
+),
+liked AS (
+    SELECT page_id
+    FROM   likes 
+    WHERE  user_id=3
+),
+friend_points AS (
+    SELECT   user_id, SUM(3) AS points
+    FROM     friends
+    WHERE    friend_id IN (SELECT friend_id FROM already_friends)
+    GROUP BY 1
+),
+like_points AS (
+    SELECT   user_id, SUM(2) AS points 
+    FROM     likes 
+    WHERE    page_id IN (SELECT page_id FROM liked)
+    GROUP BY 1
+)
+SELECT u.name AS potential_friend_name, SUM(points) AS friendship_points
+FROM (
+        SELECT user_id, points 
+        FROM   friend_points 
+        UNION 
+        SELECT user_id, points 
+        FROM   like_points 
+) f LEFT JOIN users u ON f.user_id = u.user_id
+WHERE    u.user_id NOT IN (SELECT friend_id FROM already_friends) AND 
+         u.user_id NOT IN (SELECT blocked_id FROM blocked) AND
+         u.user_id != 3
+GROUP BY 1
+ORDER BY 2, 1
+
+