SQL_DS_collections, Sql Server

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/*
CREATE TABLE Activity
    ([user_id] int, [page] varchar(25), [unix_timestamp] int)
;
    
INSERT INTO Activity
    ([user_id], [page], [unix_timestamp])
VALUES
    (2, 'home_page', 1451606400),
    (3, 'home_page', 1451606402),
    (3, 'search', 1451606404),
    (4, 'home_page', 1451606407),
    (4, 'payment_page', 1451606423),
    (4, 'product_page', 1451606419),
    (4, 'search', 1451606418),
    (5, 'home_page', 1451606425),
    (7, 'home_page', 1451606427),
    (8, 'home_page', 1451606437),
    (9, 'home_page', 1451606439),
    (13, 'home_page', 1451606441),
    (14, 'home_page', 1451606449),
    (15, 'search', 1451606465),
    (15, 'home_page', 1451606458),
    (17, 'home_page', 1451606470),
    (21, 'home_page', 1451606480),
    (22, 'home_page', 1451606484),
    (23, 'home_page', 1451606488),
    (24, 'home_page', 1451606498),
    (24, 'search', 1451606504),
    (25, 'home_page', 1451606509),
    (26, 'home_page', 1451606511),
    (27, 'home_page', 1451606521),
    (27, 'search', 1451606522),
    (28, 'home_page', 1451606524),
    (29, 'home_page', 1451606530),
    (30, 'home_page', 1451606540),
    (31, 'home_page', 1451606545),
    (33, 'home_page', 1451606546),
    (37, 'home_page', 1451606548),
    (39, 'home_page', 1451606549),
    (42, 'home_page', 1451606550),
    (43, 'home_page', 1451606552),
    (46, 'home_page', 1451606553),
    (47, 'home_page', 1451606556),
    (51, 'home_page', 1451606574),
    (51, 'payment_page', 1451606590),
    (51, 'search', 1451606575),
    (51, 'product_page', 1451606582),
    (52, 'search', 1451606596),
    (52, 'home_page', 1451606595),
    (53, 'home_page', 1451606601),
    (54, 'home_page', 1451606602),
    (55, 'home_page', 1451606612),
    (55, 'search', 1451606613),
    (57, 'home_page', 1451606615),
    (60, 'home_page', 1451606616),
    (60, 'search', 1451606617),
    (62, 'home_page', 1451606621),
    (63, 'home_page', 1451606622),
    (64, 'search', 1451606629),
    (64, 'home_page', 1451606624),
    (66, 'product_page', 1451606632),
    (66, 'home_page', 1451606630),
    (66, 'search', 1451606631),
    (69, 'home_page', 1451606633),
    (70, 'search', 1451606636),
    (70, 'home_page', 1451606634),
    (71, 'home_page', 1451606639),
    (72, 'home_page', 1451606642),
    (73, 'home_page', 1451606646),
    (76, 'search', 1451606657),
    (76, 'home_page', 1451606655),
    (77, 'search', 1451606670),
    (77, 'home_page', 1451606667),
    (78, 'product_page', 1451606691),
    (78, 'search', 1451606684),
    (78, 'payment_confirmation_page', 1451606704),
    (78, 'home_page', 1451606677),
    (78, 'payment_page', 1451606694),
    (79, 'home_page', 1451606705),
    (81, 'search', 1451606713),
    (81, 'home_page', 1451606712),
    (81, 'payment_page', 1451606721),
    (81, 'product_page', 1451606716),
    (82, 'home_page', 1451606726),
    (82, 'product_page', 1451606732),
    (82, 'search', 1451606730),
    (83, 'home_page', 1451606735),
    (84, 'home_page', 1451606736),
    (86, 'home_page', 1451606750),
    (87, 'home_page', 1451606755),
    (87, 'product_page', 1451606764),
    (87, 'search', 1451606759),
    (89, 'home_page', 1451606766),
    (90, 'home_page', 1451606773),
    (92, 'home_page', 1451606778),
    (92, 'search', 1451606786),
    (93, 'home_page', 1451606790),
    (95, 'home_page', 1451606792),
    (96, 'home_page', 1451606793),
    (96, 'search', 1451606802),
    (96, 'payment_page', 1451606807),
    (96, 'product_page', 1451606806),
    (97, 'search', 1451606831),
    (97, 'product_page', 1451606835),
    (97, 'home_page', 1451606809),
    (98, 'home_page', 1451606837),
    (100, 'home_page', 1451606842),
    (100, 'search', 1451606845),
    (103, 'home_page', 1451606846),
    (106, 'home_page', 1451606851),
    (108, 'home_page', 1451606854),
    (111, 'search', 1451606860),
    (111, 'home_page', 1451606856),
    (112, 'home_page', 1451606867),
    (113, 'home_page', 1451606871),
    (114, 'search', 1451606883),
    (114, 'home_page', 1451606881),
    (115, 'home_page', 1451606894),
    (115, 'search', 1451606895),
    (115, 'payment_page', 1451606907),
    (115, 'product_page', 1451606906),
    (116, 'home_page', 1451606909),
    (118, 'home_page', 1451606913),
    (119, 'home_page', 1451606926),
    (120, 'search', 1451606931),
    (120, 'home_page', 1451606930),
    (122, 'home_page', 1451606936),
    (123, 'home_page', 1451606939),
    (124, 'home_page', 1451606945),
    (125, 'home_page', 1451606975),
    (125, 'search', 1451606977),
    (126, 'home_page', 1451606978),
    (126, 'search', 1451606979),
    (127, 'home_page', 1451606999),
    (128, 'home_page', 1451607004),
    (130, 'home_page', 1451607006),
    (130, 'search', 1451607007),
    (131, 'home_page', 1451607013),
    (133, 'home_page', 1451607016),
    (134, 'search', 1451607032),
    (134, 'home_page', 1451607021),
    (135, 'home_page', 1451607033),
    (135, 'search', 1451607046),
    (136, 'search', 1451607055),
    (136, 'product_page', 1451607057),
    (136, 'home_page', 1451607050),
    (140, 'home_page', 1451607058),
    (142, 'home_page', 1451607068),
    (143, 'home_page', 1451607070),
    (144, 'home_page', 1451607072),
    (145, 'home_page', 1451607076),
    (145, 'search', 1451607091),
    (145, 'product_page', 1451607115),
    (148, 'home_page', 1451607120),
    (150, 'search', 1451607123),
    (150, 'home_page', 1451607121),
    (151, 'home_page', 1451607125),
    (152, 'home_page', 1451607129),
    (153, 'home_page', 1451607147),
    (154, 'home_page', 1451607149),
    (156, 'home_page', 1451607151),
    (159, 'search', 1451607157),
    (159, 'home_page', 1451607154),
    (161, 'home_page', 1451607163),
    (163, 'home_page', 1451607165),
    (163, 'product_page', 1451607174),
    (163, 'payment_page', 1451607185),
    (163, 'search', 1451607173),
    (164, 'home_page', 1451607196),
    (167, 'search', 1451607217),
    (167, 'home_page', 1451607200),
    (168, 'home_page', 1451607221),
    (168, 'search', 1451607239),
    (169, 'home_page', 1451607242),
    (170, 'home_page', 1451607261),
    (171, 'home_page', 1451607265),
    (173, 'search', 1451607286),
    (173, 'home_page', 1451607272),
    (173, 'product_page', 1451607288),
    (177, 'home_page', 1451607290),
    (179, 'home_page', 1451607293),
    (181, 'home_page', 1451607309),
    (183, 'home_page', 1451607310),
    (183, 'search', 1451607311),
    (185, 'home_page', 1451607317),
    (186, 'home_page', 1451607319),
    (187, 'home_page', 1451607323),
    (187, 'search', 1451607325),
    (188, 'home_page', 1451607329),
    (191, 'home_page', 1451607332),
    (192, 'home_page', 1451607335),
    (193, 'home_page', 1451607340),
    (194, 'home_page', 1451607342),
    (195, 'search', 1451607358),
    (195, 'home_page', 1451607349),
    (198, 'home_page', 1451607368),
    (200, 'home_page', 1451607380),
    (200, 'search', 1451607387),
    (201, 'home_page', 1451607393),
    (202, 'home_page', 1451607395),
    (204, 'home_page', 1451607396),
    (207, 'home_page', 1451607401),
    (208, 'home_page', 1451607404),
    (212, 'home_page', 1451607409),
    (213, 'home_page', 1451607411),
    (217, 'home_page', 1451607421),
    (217, 'search', 1451607426)
;

-- For each user_id, find the difference between the last action and the second last action. 
-- Action here is defined as visiting a page. If the user has just one action, you can either remove her from the final results or 
-- keep that user_id and have NULL as time difference between the two actions.

----------------- sol1 ---------------------
WITH ActivityRank AS (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY unix_timestamp DESC) AS time_rank
--    LAG(unix_timestamp,1) OVER(PARTITION BY user_id ORDER BY unix_timestamp DESC) AS lag
    FROM Activity),
    LastTwoActivities AS (
        SELECT *
        FROM ActivityRank
        WHERE time_rank<=2)
 SELECT a.user_id, a.unix_timestamp - b.unix_timestamp AS time_diff
 FROM LastTwoActivities AS a, LastTwoActivities AS b
 WHERE a.user_id = b.user_id AND a.time_rank+1 = b.time_rank;

------------- sol2 ------------------

WITH ActivityRank AS (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY unix_timestamp DESC) AS time_rank,
    LAG(unix_timestamp,1) OVER(PARTITION BY user_id ORDER BY unix_timestamp) AS lag1_time
    FROM Activity),
    LastTwoActivities AS (
        SELECT *
        FROM ActivityRank
        WHERE time_rank=1)
 SELECT user_id, unix_timestamp - lag1_time AS time_diff
 FROM LastTwoActivities 
*/
---------------------------------
------------------ Q2 --------------------
---------------------------------

CREATE TABLE Mobile
    ([user_id] int, [page] varchar(13))
;
    
INSERT INTO Mobile
    ([user_id], [page])
VALUES
    (1, 'page_3_mobile'),
    (1, 'page_2_mobile'),
    (2, 'page_7_mobile'),
    (4, 'page_2_mobile'),
    (5, 'page_3_mobile'),
    (7, 'page_4_mobile'),
    (7, 'page_4_mobile'),
    (8, 'page_3_mobile'),
    (9, 'page_4_mobile'),
    (9, 'page_8_mobile'),
    (10, 'page_1_mobile'),
    (12, 'page_8_mobile'),
    (12, 'page_7_mobile'),
    (12, 'page_1_mobile'),
    (13, 'page_3_mobile'),
    (14, 'page_1_mobile'),
    (14, 'page_4_mobile'),
    (16, 'page_8_mobile'),
    (16, 'page_8_mobile'),
    (16, 'page_5_mobile'),
    (17, 'page_2_mobile'),
    (17, 'page_8_mobile'),
    (17, 'page_2_mobile'),
    (18, 'page_6_mobile'),
    (18, 'page_8_mobile'),
    (19, 'page_8_mobile'),
    (20, 'page_4_mobile'),
    (21, 'page_6_mobile'),
    (23, 'page_1_mobile'),
    (24, 'page_1_mobile'),
    (24, 'page_4_mobile'),
    (25, 'page_5_mobile'),
    (25, 'page_8_mobile'),
    (26, 'page_7_mobile'),
    (26, 'page_1_mobile'),
    (26, 'page_4_mobile'),
    (27, 'page_6_mobile'),
    (29, 'page_3_mobile'),
    (29, 'page_5_mobile'),
    (30, 'page_4_mobile'),
    (33, 'page_1_mobile'),
    (33, 'page_1_mobile'),
    (34, 'page_7_mobile'),
    (34, 'page_3_mobile'),
    (34, 'page_5_mobile'),
    (34, 'page_3_mobile'),
    (34, 'page_5_mobile'),
    (35, 'page_8_mobile'),
    (35, 'page_2_mobile'),
    (35, 'page_3_mobile'),
    (36, 'page_7_mobile'),
    (36, 'page_7_mobile'),
    (37, 'page_6_mobile'),
    (38, 'page_2_mobile'),
    (38, 'page_5_mobile'),
    (39, 'page_6_mobile')
;

CREATE TABLE Web
    ([user_id] int, [page] varchar(10))
;
    
INSERT INTO Web
    ([user_id], [page])
VALUES
    (1, 'page_8_web'),
    (4, 'page_5_web'),
    (4, 'page_6_web'),
    (5, 'page_5_web'),
    (6, 'page_3_web'),
    (9, 'page_5_web'),
    (11, 'page_7_web'),
    (13, 'page_6_web'),
    (13, 'page_7_web'),
    (15, 'page_3_web'),
    (15, 'page_6_web'),
    (16, 'page_1_web'),
    (17, 'page_6_web'),
    (17, 'page_3_web'),
    (18, 'page_2_web'),
    (22, 'page_2_web'),
    (23, 'page_6_web'),
    (24, 'page_4_web'),
    (26, 'page_4_web'),
    (26, 'page_5_web'),
    (27, 'page_6_web'),
    (28, 'page_5_web'),
    (28, 'page_7_web'),
    (30, 'page_1_web'),
    (31, 'page_4_web'),
    (31, 'page_7_web'),
    (32, 'page_3_web'),
    (33, 'page_8_web'),
    (35, 'page_6_web'),
    (35, 'page_1_web'),
    (36, 'page_1_web'),
    (36, 'page_2_web'),
    (36, 'page_8_web'),
    (37, 'page_2_web'),
    (37, 'page_2_web'),
    (38, 'page_7_web'),
    (38, 'page_5_web')
;
-- We have two tables. One table has all mobile actions, i.e. all pages visited by the users on mobile. 
-- The other table has all web actions, i.e. all pages visited on web by the users.
-- Write a query that returns the percentage of users who only visited mobile, only web and both. That is, the percentage of users who are only in the mobile table, only in the web table and in both tables. The sum of the percentages should return 1.
/*

------- sol1 -----------
WITH mobile_only_cnt AS (
    SELECT COUNT(DISTINCT user_id) AS users
    FROM Mobile
    WHERE user_id NOT IN (SELECT user_id FROM Web)),
    web_only_cnt AS (     
    SELECT COUNT(user_id) AS users
    FROM Web
    WHERE user_id NOT IN (SELECT user_id FROM Mobile)),
    both_cnt AS (
    SELECT COUNT(DISTINCT a.user_id) AS users
    FROM Mobile AS a INNER JOIN Web AS b ON a.user_id = b.user_id),
union_cnt AS (
    SELECT COUNT(DISTINCT user_id) AS users
    FROM (SELECT user_id 
          FROM Web 
          UNION 
          SELECT user_id 
          FROM Mobile) AS t)                    
SELECT a.users*1.00/b.users AS mobile, c.users*1.00/b.users AS web, d.users*1.00/b.users AS both
FROM mobile_only_cnt AS a CROSS JOIN union_cnt AS b CROSS JOIN web_only_cnt AS c CROSS JOIN both_cnt AS d

--------- sol2 ------------
SELECT SUM(CASE WHEN a.user_id IS NULL THEN 1 ELSE 0 END)*1.00/COUNT(*) AS web_only,
SUM(CASE WHEN b.user_id IS NULL THEN 1 ELSE 0 END)*1.00/COUNT(*) AS mobile_only,
SUM(CASE WHEN a.user_id IS NOT NULL AND b.user_id IS NOT NULL THEN 1 ELSE 0 END)*1.00/COUNT(*) AS both
FROM
(SELECT user_id
 FROM Mobile
 GROUP BY user_id) AS a FULL OUTER JOIN 
(SELECT user_id
 FROM Web
 GROUP BY user_id) AS b
ON a.user_id = b.user_id

*/
------------------------------------------
------------------ Q3 -------------------
-------------------------------------------

CREATE TABLE Purchases
    ([user_id] int, [date] datetime)
;
    
INSERT INTO Purchases
    ([user_id], [date])
VALUES
    (1, '2015-01-31 21:37:00'),
    (1, '2015-02-27 02:53:00'),
    (1, '2015-04-06 02:54:00'),
    (1, '2015-04-15 05:30:00'),
    (1, '2015-05-01 18:21:00'),
    (1, '2015-05-08 10:44:00'),
    (1, '2015-05-30 00:08:00'),
    (1, '2015-09-20 17:09:00'),
    (1, '2015-10-21 01:41:00'),
    (1, '2015-10-21 06:20:00'),
    (1, '2015-12-15 14:27:00'),
    (1, '2015-12-16 16:16:00'),
    (2, '2015-01-03 23:44:00'),
    (2, '2015-01-08 09:05:00'),
    (2, '2015-05-06 02:40:00'),
    (2, '2015-06-01 00:42:00'),
    (2, '2015-08-20 02:14:00'),
    (2, '2015-10-06 06:54:00'),
    (2, '2015-10-06 15:32:00'),
    (2, '2015-11-01 07:23:00'),
    (2, '2015-11-04 16:56:00'),
    (3, '2015-04-01 15:31:00'),
    (3, '2015-04-07 11:59:00'),
    (3, '2015-06-08 16:34:00'),
    (3, '2015-07-28 00:16:00'),
    (3, '2015-09-09 20:36:00'),
    (3, '2015-09-26 03:57:00'),
    (3, '2015-10-03 17:14:00'),
    (3, '2015-10-17 09:07:00'),
    (3, '2015-10-23 13:32:00'),
    (3, '2015-10-29 22:41:00'),
    (3, '2015-11-04 14:01:00'),
    (3, '2015-12-02 00:56:00'),
    (3, '2015-12-15 17:17:00'),
    (3, '2015-12-22 04:03:00'),
    (4, '2015-01-15 12:34:00'),
    (4, '2015-04-15 02:13:00'),
    (4, '2015-05-18 04:28:00'),
    (4, '2015-05-21 21:17:00'),
    (4, '2015-05-22 20:45:00'),
    (4, '2015-06-10 02:55:00'),
    (4, '2015-06-27 15:31:00'),
    (4, '2015-09-13 04:00:00'),
    (4, '2015-09-20 02:44:00'),
    (4, '2015-09-25 12:36:00'),
    (4, '2015-11-19 06:33:00'),
    (5, '2015-01-13 20:00:00'),
    (5, '2015-02-09 18:41:00'),
    (5, '2015-04-09 02:39:00'),
    (5, '2015-04-26 05:26:00'),
    (5, '2015-05-02 20:53:00'),
    (5, '2015-05-05 08:25:00'),
    (5, '2015-05-19 10:55:00'),
    (5, '2015-08-25 03:30:00'),
    (5, '2015-09-03 16:06:00'),
    (5, '2015-09-18 06:25:00'),
    (5, '2015-11-15 11:19:00'),
    (5, '2015-11-18 12:34:00'),
    (5, '2015-12-26 03:52:00'),
    (6, '2015-02-16 11:48:00'),
    (6, '2015-02-16 13:35:00'),
    (6, '2015-02-24 15:44:00'),
    (6, '2015-03-03 10:04:00'),
    (6, '2015-07-06 11:50:00'),
    (6, '2015-08-14 10:49:00'),
    (6, '2015-09-11 04:38:00'),
    (6, '2015-11-03 00:53:00'),
    (6, '2015-11-13 18:27:00'),
    (6, '2015-12-30 00:53:00'),
    (7, '2015-01-02 13:34:00'),
    (7, '2015-01-18 03:53:00'),
    (7, '2015-01-20 16:10:00'),
    (7, '2015-02-27 03:08:00'),
    (7, '2015-03-15 08:49:00'),
    (7, '2015-04-28 10:19:00'),
    (7, '2015-05-25 13:00:00'),
    (7, '2015-06-11 10:36:00'),
    (7, '2015-06-28 12:29:00'),
    (7, '2015-09-10 02:46:00'),
    (7, '2015-10-01 19:31:00'),
    (7, '2015-10-31 14:05:00'),
    (7, '2015-12-19 23:13:00'),
    (7, '2015-12-26 07:20:00'),
    (8, '2015-05-14 08:23:00'),
    (8, '2015-07-24 12:33:00'),
    (8, '2015-11-09 15:14:00'),
    (8, '2015-12-10 20:53:00'),
    (9, '2015-01-23 00:15:00'),
    (9, '2015-04-17 22:54:00'),
    (9, '2015-06-25 02:14:00'),
    (9, '2015-10-16 15:03:00'),
    (9, '2015-10-23 16:33:00'),
    (10, '2015-01-31 02:39:00'),
    (10, '2015-04-24 01:56:00'),
    (10, '2015-06-21 13:18:00'),
    (10, '2015-07-22 08:58:00'),
    (10, '2015-08-13 20:29:00'),
    (10, '2015-08-23 09:02:00'),
    (10, '2015-10-21 20:52:00'),
    (10, '2015-11-05 20:48:00'),
    (10, '2015-12-21 01:09:00'),
    (10, '2015-12-24 12:52:00'),
    (11, '2015-02-12 21:35:00'),
    (11, '2015-05-09 14:40:00'),
    (11, '2015-05-15 05:32:00'),
    (11, '2015-05-19 12:19:00'),
    (11, '2015-05-31 18:49:00'),
    (11, '2015-06-22 12:38:00'),
    (11, '2015-09-17 12:26:00'),
    (11, '2015-09-19 06:10:00'),
    (11, '2015-10-29 21:33:00'),
    (11, '2015-11-10 05:31:00'),
    (11, '2015-12-29 12:13:00'),
    (12, '2015-01-08 06:27:00'),
    (12, '2015-01-09 04:12:00'),
    (12, '2015-01-18 09:40:00'),
    (12, '2015-02-18 13:10:00'),
    (12, '2015-04-14 23:39:00'),
    (12, '2015-04-21 17:23:00'),
    (12, '2015-06-23 04:08:00'),
    (12, '2015-07-22 18:35:00'),
    (12, '2015-07-27 19:01:00'),
    (12, '2015-10-01 20:24:00'),
    (12, '2015-10-08 10:51:00'),
    (12, '2015-10-14 16:56:00'),
    (12, '2015-10-15 08:39:00'),
    (12, '2015-10-21 07:24:00'),
    (12, '2015-11-12 11:16:00'),
    (13, '2015-01-05 17:26:00'),
    (13, '2015-03-30 00:55:00'),
    (13, '2015-05-15 10:47:00'),
    (13, '2015-06-13 18:56:00'),
    (13, '2015-06-21 10:07:00'),
    (13, '2015-12-15 05:45:00'),
    (14, '2015-01-31 18:07:00'),
    (14, '2015-06-07 18:40:00'),
    (14, '2015-08-08 07:28:00'),
    (14, '2015-08-30 12:08:00'),
    (14, '2015-09-10 00:34:00'),
    (14, '2015-10-30 01:52:00'),
    (14, '2015-12-01 10:54:00'),
    (14, '2015-12-15 16:56:00'),
    (14, '2015-12-16 08:18:00'),
    (15, '2015-01-12 14:39:00'),
    (15, '2015-02-13 23:08:00'),
    (15, '2015-03-14 23:12:00'),
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;

-- We define as power users those users who bought at least 10 products. 
-- Write a query that returns for each user on which day they became a power user. That is, for each user, on which day they bought the 10th item.
-- The table below represents transactions. That is, each row means that the corresponding user has bought something on that date.

/*
SELECT user_id, date
FROM
(SELECT *,
ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY date) AS date_rank
FROM Purchases) AS t
WHERE date_rank=10
*/

-----------------------------------
---------------- Q4 --------------------
---------------------------------------

CREATE TABLE April
    ([user_id] int, [date] datetime, [transaction_amount] int)
;
    
INSERT INTO April
    ([user_id], [date], [transaction_amount])
VALUES
    (4, '2015-04-20 00:00:00', 93),
    (8, '2015-04-07 00:00:00', 96),
    (9, '2015-04-17 00:00:00', 89),
    (9, '2015-04-18 00:00:00', 70),
    (10, '2015-04-07 00:00:00', 15),
    (11, '2015-04-03 00:00:00', 71),
    (12, '2015-04-14 00:00:00', 79),
    (16, '2015-04-14 00:00:00', 60),
    (17, '2015-04-08 00:00:00', 92),
    (18, '2015-04-03 00:00:00', 54),
    (18, '2015-04-08 00:00:00', 23),
    (19, '2015-04-10 00:00:00', 22),
    (23, '2015-04-07 00:00:00', 33),
    (30, '2015-04-06 00:00:00', 50),
    (32, '2015-04-22 00:00:00', 43),
    (33, '2015-04-21 00:00:00', 45),
    (38, '2015-04-03 00:00:00', 142),
    (41, '2015-04-13 00:00:00', 70),
    (41, '2015-04-24 00:00:00', 34),
    (42, '2015-04-09 00:00:00', 110),
    (42, '2015-04-19 00:00:00', 94),
    (43, '2015-04-25 00:00:00', 22),
    (43, '2015-04-25 00:00:00', 38),
    (45, '2015-04-19 00:00:00', 61),
    (49, '2015-04-28 00:00:00', 60),
    (50, '2015-04-09 00:00:00', 77),
    (52, '2015-04-20 00:00:00', 42),
    (55, '2015-04-01 00:00:00', 103),
    (55, '2015-04-11 00:00:00', 125),
    (60, '2015-04-16 00:00:00', 84),
    (63, '2015-04-06 00:00:00', 67),
    (66, '2015-04-27 00:00:00', 68),
    (70, '2015-04-05 00:00:00', 28),
    (71, '2015-04-02 00:00:00', 65),
    (72, '2015-04-03 00:00:00', 49),
    (77, '2015-04-07 00:00:00', 54),
    (81, '2015-04-24 00:00:00', 67),
    (82, '2015-04-14 00:00:00', 39),
    (82, '2015-04-23 00:00:00', 46),
    (84, '2015-04-15 00:00:00', 92),
    (85, '2015-04-05 00:00:00', 70),
    (89, '2015-04-10 00:00:00', 18),
    (90, '2015-04-12 00:00:00', 92),
    (94, '2015-04-08 00:00:00', 58),
    (95, '2015-04-02 00:00:00', 76),
    (97, '2015-04-29 00:00:00', 53),
    (99, '2015-04-22 00:00:00', 49),
    (102, '2015-04-24 00:00:00', 72),
    (103, '2015-04-07 00:00:00', 77),
    (103, '2015-04-16 00:00:00', 121),
    (105, '2015-04-08 00:00:00', 57),
    (108, '2015-04-21 00:00:00', 102),
    (108, '2015-04-26 00:00:00', 38),
    (111, '2015-04-13 00:00:00', 70),
    (112, '2015-04-10 00:00:00', 67),
    (112, '2015-04-23 00:00:00', 15),
    (114, '2015-04-14 00:00:00', 68),
    (115, '2015-04-27 00:00:00', 62),
    (118, '2015-04-09 00:00:00', 37),
    (123, '2015-04-24 00:00:00', 79),
    (125, '2015-04-21 00:00:00', 68),
    (125, '2015-04-24 00:00:00', 79),
    (125, '2015-04-27 00:00:00', 55),
    (129, '2015-04-16 00:00:00', 12),
    (129, '2015-04-23 00:00:00', 39),
    (130, '2015-04-25 00:00:00', 76),
    (131, '2015-04-14 00:00:00', 23),
    (135, '2015-04-15 00:00:00', 120),
    (136, '2015-04-05 00:00:00', 83),
    (137, '2015-04-02 00:00:00', 69),
    (137, '2015-04-26 00:00:00', 53),
    (141, '2015-04-02 00:00:00', 116),
    (142, '2015-04-16 00:00:00', 46),
    (144, '2015-04-13 00:00:00', 98),
    (145, '2015-04-10 00:00:00', 77),
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    (150, '2015-04-07 00:00:00', 72),
    (159, '2015-04-12 00:00:00', 131),
    (160, '2015-04-30 00:00:00', 74),
    (163, '2015-04-30 00:00:00', 77),
    (164, '2015-04-16 00:00:00', 43),
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    (170, '2015-04-07 00:00:00', 119),
    (170, '2015-04-09 00:00:00', 85),
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    (253, '2015-04-14 00:00:00', 44),
    (254, '2015-04-14 00:00:00', 57),
    (254, '2015-04-15 00:00:00', 74),
    (255, '2015-04-03 00:00:00', 81),
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    (255, '2015-04-08 00:00:00', 16),
    (259, '2015-04-27 00:00:00', 46),
    (260, '2015-04-17 00:00:00', 56),
    (261, '2015-04-11 00:00:00', 46),
    (262, '2015-04-21 00:00:00', 87),
    (266, '2015-04-21 00:00:00', 94),
    (270, '2015-04-17 00:00:00', 66),
    (270, '2015-04-23 00:00:00', 54),
    (271, '2015-04-01 00:00:00', 55),
    (271, '2015-04-07 00:00:00', 57),
    (273, '2015-04-06 00:00:00', 70),
    (273, '2015-04-13 00:00:00', 87),
    (273, '2015-04-24 00:00:00', 43),
    (274, '2015-04-12 00:00:00', 50),
    (274, '2015-04-15 00:00:00', 34),
    (275, '2015-04-18 00:00:00', 34),
    (275, '2015-04-18 00:00:00', 100)
;

CREATE TABLE March
    ([user_id] int, [date] datetime, [transaction_amount] int)
;
    
INSERT INTO March
    ([user_id], [date], [transaction_amount])
VALUES
    (2, '2015-03-13 00:00:00', 67),
    (3, '2015-03-31 00:00:00', 26),
    (4, '2015-03-28 00:00:00', 63),
    (5, '2015-03-01 00:00:00', 45),
    (6, '2015-03-15 00:00:00', 32),
    (8, '2015-03-06 00:00:00', 66),
    (8, '2015-03-14 00:00:00', 73),
    (11, '2015-03-06 00:00:00', 91),
    (12, '2015-03-24 00:00:00', 36),
    (12, '2015-03-25 00:00:00', 14),
    (13, '2015-03-24 00:00:00', 22),
    (15, '2015-03-05 00:00:00', 113),
    (23, '2015-03-01 00:00:00', 19),
    (24, '2015-03-06 00:00:00', 34),
    (26, '2015-03-17 00:00:00', 53),
    (28, '2015-03-03 00:00:00', 33),
    (28, '2015-03-17 00:00:00', 77),
    (29, '2015-03-09 00:00:00', 37),
    (34, '2015-03-20 00:00:00', 73),
    (42, '2015-03-17 00:00:00', 88),
    (45, '2015-03-26 00:00:00', 112),
    (46, '2015-03-20 00:00:00', 36),
    (50, '2015-03-07 00:00:00', 73),
    (50, '2015-03-13 00:00:00', 41),
    (55, '2015-03-03 00:00:00', 62),
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    (60, '2015-03-13 00:00:00', 26),
    (60, '2015-03-18 00:00:00', 15),
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    (66, '2015-03-09 00:00:00', 26),
    (70, '2015-03-14 00:00:00', 81),
    (71, '2015-03-11 00:00:00', 10),
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    (75, '2015-03-30 00:00:00', 71),
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    (80, '2015-03-26 00:00:00', 63),
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    (88, '2015-03-17 00:00:00', 64),
    (89, '2015-03-27 00:00:00', 62),
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    (102, '2015-03-21 00:00:00', 65),
    (103, '2015-03-31 00:00:00', 39),
    (105, '2015-03-01 00:00:00', 48),
    (110, '2015-03-30 00:00:00', 72),
    (112, '2015-03-08 00:00:00', 31),
    (115, '2015-03-30 00:00:00', 13),
    (120, '2015-03-05 00:00:00', 29),
    (122, '2015-03-23 00:00:00', 72),
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    (127, '2015-03-08 00:00:00', 22),
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    (132, '2015-03-04 00:00:00', 38),
    (133, '2015-03-26 00:00:00', 69),
    (134, '2015-03-17 00:00:00', 55),
    (136, '2015-03-12 00:00:00', 75),
    (137, '2015-03-02 00:00:00', 71),
    (138, '2015-03-12 00:00:00', 54),
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    (139, '2015-03-16 00:00:00', 19),
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    (154, '2015-03-31 00:00:00', 39),
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    (157, '2015-03-06 00:00:00', 94),
    (157, '2015-03-16 00:00:00', 60),
    (159, '2015-03-30 00:00:00', 70),
    (162, '2015-03-25 00:00:00', 90),
    (166, '2015-03-08 00:00:00', 34),
    (166, '2015-03-16 00:00:00', 11),
    (167, '2015-03-16 00:00:00', 115),
    (169, '2015-03-20 00:00:00', 58),
    (173, '2015-03-10 00:00:00', 70),
    (177, '2015-03-05 00:00:00', 37),
    (177, '2015-03-17 00:00:00', 53),
    (177, '2015-03-27 00:00:00', 50),
    (178, '2015-03-01 00:00:00', 45),
    (181, '2015-03-04 00:00:00', 22),
    (183, '2015-03-06 00:00:00', 113),
    (184, '2015-03-07 00:00:00', 40),
    (184, '2015-03-19 00:00:00', 17),
    (184, '2015-03-23 00:00:00', 45),
    (186, '2015-03-14 00:00:00', 92),
    (186, '2015-03-15 00:00:00', 29),
    (187, '2015-03-03 00:00:00', 58),
    (187, '2015-03-10 00:00:00', 74),
    (188, '2015-03-10 00:00:00', 94),
    (188, '2015-03-13 00:00:00', 42),
    (190, '2015-03-12 00:00:00', 33),
    (191, '2015-03-11 00:00:00', 61),
    (191, '2015-03-22 00:00:00', 43),
    (191, '2015-03-27 00:00:00', 49),
    (194, '2015-03-09 00:00:00', 24),
    (195, '2015-03-07 00:00:00', 44),
    (201, '2015-03-07 00:00:00', 10),
    (202, '2015-03-10 00:00:00', 70),
    (202, '2015-03-21 00:00:00', 76),
    (203, '2015-03-06 00:00:00', 57),
    (203, '2015-03-08 00:00:00', 46),
    (204, '2015-03-23 00:00:00', 29),
    (205, '2015-03-30 00:00:00', 52),
    (207, '2015-03-20 00:00:00', 47),
    (208, '2015-03-16 00:00:00', 57),
    (210, '2015-03-18 00:00:00', 13),
    (211, '2015-03-27 00:00:00', 104),
    (213, '2015-03-23 00:00:00', 38),
    (218, '2015-03-06 00:00:00', 41),
    (218, '2015-03-24 00:00:00', 74),
    (218, '2015-03-25 00:00:00', 13),
    (221, '2015-03-23 00:00:00', 58),
    (224, '2015-03-08 00:00:00', 77),
    (225, '2015-03-10 00:00:00', 90),
    (232, '2015-03-25 00:00:00', 74),
    (233, '2015-03-25 00:00:00', 56),
    (234, '2015-03-30 00:00:00', 42),
    (235, '2015-03-08 00:00:00', 42),
    (238, '2015-03-05 00:00:00', 29),
    (239, '2015-03-03 00:00:00', 11),
    (241, '2015-03-21 00:00:00', 68),
    (242, '2015-03-02 00:00:00', 34),
    (242, '2015-03-15 00:00:00', 92),
    (242, '2015-03-17 00:00:00', 17),
    (242, '2015-03-20 00:00:00', 35),
    (245, '2015-03-24 00:00:00', 121),
    (250, '2015-03-12 00:00:00', 57),
    (256, '2015-03-09 00:00:00', 108),
    (258, '2015-03-29 00:00:00', 77),
    (259, '2015-03-03 00:00:00', 27),
    (259, '2015-03-25 00:00:00', 78),
    (260, '2015-03-08 00:00:00', 80),
    (260, '2015-03-10 00:00:00', 78),
    (260, '2015-03-26 00:00:00', 103),
    (265, '2015-03-17 00:00:00', 44),
    (266, '2015-03-10 00:00:00', 83),
    (269, '2015-03-28 00:00:00', 31),
    (271, '2015-03-26 00:00:00', 41),
    (272, '2015-03-17 00:00:00', 39)
;

-- We have two tables. One table has all $ transactions from users during the month of March and one for the month of April.

-- Write a query that returns the total amount of money spent by each user. That is, the sum of the column transaction_amount for each user over both tables.
-- Write a query that returns day by day the cumulative sum of money spent by each user. 
-- That is, each day a user had a transcation, we should have how much money she has spent in total until that day. 
-- Obviously, the last day cumulative sum should match the numbers from the previous bullet point.
/*
SELECT CASE WHEN a.user_id IS NULL THEN b.user_id ELSE a.user_id END AS user_id,
ISNULL(a.total_trans,0)+ISNULL(b.total_trans,0) AS total_trans
FROM
(SELECT user_id, SUM(transaction_amount) AS total_trans
FROM March
GROUP BY user_id) AS a FULL OUTER JOIN
(SELECT user_id, SUM(transaction_amount) AS total_trans
 FROM April
 GROUp BY user_id) AS b ON a.user_id = b.user_id
*/

/*
-------- sol1 --------------
WITH t AS (
    SELECT *
    FROM March
    UNION ALL
    SELECT *
    FROM April)

SELECT b.user_id, b.date, SUM(a.transaction_amount) AS running_trans
FROM t AS a, t AS b
WHERE a.user_id = b.user_id AND a.date<=b.date
GROUP BY b.user_id, b.date
ORDER BY b.user_id, b.date

----------- sol2 ------------

SELECt *, SUM(transaction_amount) OVER(PARTITION BY user_id ORDER BY date) AS running_trans
FROM
(SELECT * FROM March UNION ALL SELECT * FROM April) AS t
ORDER BY user_id, date

-------------------------------------
-------------- Q5 ---------------------
-------------------------------------

CREATE TABLE users
    ([user_id] int, [sign_up_date] datetime)
;
    
INSERT INTO users
    ([user_id], [sign_up_date])
VALUES
    (121, '2015-01-02 00:00:00'),
    (617, '2015-01-02 00:00:00'),
    (619, '2015-01-02 00:00:00'),
    (625, '2015-01-02 00:00:00'),
    (753, '2015-01-02 00:00:00'),
    (1384, '2015-01-02 00:00:00'),
    (3364, '2015-01-02 00:00:00'),
    (4820, '2015-01-02 00:00:00'),
    (4853, '2015-01-02 00:00:00'),
    (5209, '2015-01-02 00:00:00'),
    (5354, '2015-01-02 00:00:00'),
    (6118, '2015-01-02 00:00:00'),
    (6564, '2015-01-02 00:00:00'),
    (6701, '2015-01-02 00:00:00'),
    (7302, '2015-01-02 00:00:00'),
    (7864, '2015-01-02 00:00:00'),
    (8116, '2015-01-02 00:00:00'),
    (8143, '2015-01-02 00:00:00'),
    (8608, '2015-01-02 00:00:00'),
    (8675, '2015-01-02 00:00:00'),
    (9230, '2015-01-02 00:00:00'),
    (9263, '2015-01-02 00:00:00'),
    (10113, '2015-01-02 00:00:00'),
    (10287, '2015-01-02 00:00:00'),
    (10370, '2015-01-02 00:00:00'),
    (12028, '2015-01-02 00:00:00'),
    (12597, '2015-01-03 00:00:00'),
    (12826, '2015-01-03 00:00:00'),
    (13014, '2015-01-03 00:00:00'),
    (13569, '2015-01-03 00:00:00'),
    (13616, '2015-01-03 00:00:00'),
    (15005, '2015-01-03 00:00:00'),
    (15338, '2015-01-03 00:00:00'),
    (15768, '2015-01-03 00:00:00'),
    (15822, '2015-01-03 00:00:00'),
    (15960, '2015-01-03 00:00:00'),
    (16627, '2015-01-03 00:00:00'),
    (17357, '2015-01-03 00:00:00'),
    (17576, '2015-01-03 00:00:00'),
    (17697, '2015-01-03 00:00:00'),
    (19030, '2015-01-03 00:00:00'),
    (21582, '2015-01-03 00:00:00'),
    (22376, '2015-01-04 00:00:00'),
    (22530, '2015-01-04 00:00:00'),
    (23027, '2015-01-04 00:00:00'),
    (23410, '2015-01-04 00:00:00'),
    (23424, '2015-01-04 00:00:00'),
    (24027, '2015-01-04 00:00:00'),
    (24069, '2015-01-04 00:00:00')
;

CREATE TABLE transactions
    ([user_id] int, [transaction_date] datetime, [transaction_amount] int)
;
    
INSERT INTO transactions
    ([user_id], [transaction_date], [transaction_amount])
VALUES
    (121, '2015-08-10 02:56:00', 43),
    (121, '2015-05-25 17:11:00', 47),
    (121, '2015-08-05 00:13:00', 44),
    (121, '2015-04-23 09:57:00', 34),
    (121, '2015-04-29 10:39:00', 45),
    (121, '2015-08-17 01:51:00', 45),
    (121, '2015-01-01 16:45:00', 94),
    (617, '2015-09-17 14:20:00', 30),
    (617, '2015-08-23 04:56:00', 49),
    (617, '2015-07-17 10:44:00', 58),
    (617, '2015-09-01 12:08:00', 56),
    (617, '2015-01-01 17:01:00', 66),
    (619, '2015-05-20 17:12:00', 57),
    (619, '2015-07-20 02:08:00', 66),
    (619, '2015-01-01 17:12:00', 56),
    (619, '2015-07-27 11:39:00', 67),
    (619, '2015-09-20 17:24:00', 50),
    (619, '2015-06-06 08:17:00', 58),
    (619, '2015-06-14 08:50:00', 41),
    (619, '2015-07-12 14:26:00', 47),
    (625, '2015-01-01 18:34:00', 51),
    (625, '2015-09-09 14:31:00', 57),
    (625, '2015-09-17 17:37:00', 45),
    (625, '2015-04-28 04:34:00', 52),
    (625, '2015-09-26 04:22:00', 38),
    (625, '2015-05-07 01:00:00', 65),
    (753, '2015-01-01 18:55:00', 60),
    (753, '2015-08-06 15:51:00', 46),
    (753, '2015-04-25 20:40:00', 65),
    (753, '2015-05-30 08:28:00', 32),
    (753, '2015-05-28 00:24:00', 51),
    (1384, '2015-08-10 08:12:00', 38),
    (1384, '2015-01-01 19:08:00', 67),
    (1384, '2015-07-31 10:56:00', 40),
    (3364, '2015-07-25 12:40:00', 38),
    (3364, '2015-09-09 00:23:00', 33),
    (3364, '2015-05-09 12:15:00', 45),
    (3364, '2015-09-08 16:09:00', 37),
    (3364, '2015-05-24 11:26:00', 62),
    (3364, '2015-01-01 20:18:00', 69),
    (3364, '2015-04-29 20:19:00', 52),
    (4820, '2015-01-01 20:22:00', 61),
    (4820, '2015-08-27 06:31:00', 55),
    (4820, '2015-07-06 18:44:00', 39),
    (4820, '2015-07-18 07:46:00', 37),
    (4820, '2015-09-10 04:54:00', 32),
    (4853, '2015-06-03 06:08:00', 46),
    (4853, '2015-07-21 13:26:00', 33),
    (4853, '2015-04-02 06:40:00', 44),
    (4853, '2015-01-01 20:45:00', 56),
    (5209, '2015-05-03 07:42:00', 60),
    (5209, '2015-06-03 07:40:00', 38),
    (5209, '2015-04-08 14:13:00', 52),
    (5209, '2015-09-16 11:39:00', 38),
    (5209, '2015-07-25 14:25:00', 25),
    (5209, '2015-04-30 23:14:00', 55),
    (5209, '2015-06-05 02:42:00', 58),
    (5209, '2015-08-16 02:27:00', 56),
    (5209, '2015-08-29 06:39:00', 43),
    (5209, '2015-09-29 12:26:00', 59),
    (5209, '2015-01-01 21:18:00', 57),
    (5354, '2015-09-05 06:01:00', 61),
    (5354, '2015-01-01 21:35:00', 53),
    (5354, '2015-07-27 11:07:00', 65),
    (6118, '2015-04-19 09:55:00', 45),
    (6118, '2015-01-01 21:53:00', 58),
    (6118, '2015-07-08 19:17:00', 39),
    (6118, '2015-09-20 17:21:00', 61),
    (6564, '2015-08-01 15:06:00', 48),
    (6564, '2015-01-01 22:53:00', 47),
    (6564, '2015-08-26 12:33:00', 42),
    (6564, '2015-08-05 20:46:00', 68),
    (6564, '2015-09-11 07:57:00', 44),
    (6564, '2015-06-21 09:06:00', 62),
    (6564, '2015-05-22 05:08:00', 46),
    (6701, '2015-09-22 07:26:00', 47),
    (6701, '2015-05-02 15:37:00', 56),
    (6701, '2015-01-02 00:18:00', 77),
    (6701, '2015-09-05 05:35:00', 41),
    (6701, '2015-07-28 02:49:00', 69),
    (6701, '2015-05-06 15:58:00', 45),
    (6701, '2015-09-18 18:10:00', 55),
    (7302, '2015-09-16 17:30:00', 53),
    (7302, '2015-01-02 00:52:00', 61),
    (7302, '2015-05-22 21:29:00', 45),
    (7302, '2015-04-03 23:14:00', 58),
    (7302, '2015-06-23 23:02:00', 47),
    (7302, '2015-09-05 10:08:00', 72),
    (7302, '2015-08-14 14:30:00', 45),
    (7302, '2015-08-10 18:56:00', 45),
    (7302, '2015-09-28 15:02:00', 55),
    (7864, '2015-05-18 03:24:00', 59),
    (7864, '2015-07-04 11:08:00', 43),
    (7864, '2015-04-08 02:46:00', 56),
    (7864, '2015-01-02 05:07:00', 63),
    (7864, '2015-09-04 03:31:00', 51),
    (7864, '2015-09-01 12:02:00', 60),
    (8116, '2015-06-07 08:03:00', 69),
    (8116, '2015-06-10 08:43:00', 63),
    (8116, '2015-01-02 06:01:00', 65),
    (8116, '2015-09-22 21:50:00', 63),
    (8116, '2015-08-04 07:05:00', 45),
    (8143, '2015-06-23 00:14:00', 50),
    (8143, '2015-04-08 12:03:00', 56),
    (8143, '2015-04-07 02:34:00', 42),
    (8143, '2015-05-18 15:32:00', 42),
    (8143, '2015-08-09 03:26:00', 57),
    (8143, '2015-01-02 06:51:00', 54),
    (8143, '2015-08-18 14:52:00', 63),
    (8143, '2015-05-11 00:19:00', 45),
    (8608, '2015-07-06 03:07:00', 71),
    (8608, '2015-09-02 13:52:00', 54),
    (8608, '2015-07-23 12:23:00', 56),
    (8608, '2015-01-02 07:52:00', 31),
    (8608, '2015-05-18 00:05:00', 41),
    (8608, '2015-07-22 12:17:00', 53),
    (8675, '2015-05-01 00:29:00', 39),
    (8675, '2015-08-08 02:51:00', 66),
    (8675, '2015-06-17 16:55:00', 32),
    (8675, '2015-08-15 20:45:00', 53),
    (8675, '2015-01-02 10:35:00', 60),
    (9230, '2015-01-02 10:38:00', 47),
    (9230, '2015-08-11 07:50:00', 55),
    (9263, '2015-04-01 18:35:00', 76),
    (9263, '2015-09-11 08:43:00', 54),
    (9263, '2015-09-13 06:53:00', 61),
    (9263, '2015-07-22 06:29:00', 28),
    (9263, '2015-06-08 07:37:00', 26),
    (9263, '2015-07-10 05:07:00', 36),
    (9263, '2015-01-02 10:43:00', 38),
    (9263, '2015-04-25 08:28:00', 59),
    (10113, '2015-08-16 17:30:00', 47),
    (10113, '2015-01-02 10:49:00', 53),
    (10113, '2015-04-03 06:58:00', 63),
    (10113, '2015-06-20 15:22:00', 63),
    (10113, '2015-07-21 08:13:00', 49),
    (10113, '2015-04-10 12:56:00', 49),
    (10287, '2015-06-24 06:19:00', 49),
    (10287, '2015-09-25 13:59:00', 26),
    (10287, '2015-08-13 02:31:00', 49),
    (10287, '2015-01-02 13:28:00', 42),
    (10370, '2015-05-18 15:58:00', 36),
    (10370, '2015-01-02 14:55:00', 31),
    (10370, '2015-05-30 06:10:00', 53),
    (12028, '2015-01-02 15:49:00', 51),
    (12028, '2015-05-22 22:33:00', 48),
    (12028, '2015-04-21 13:21:00', 37),
    (12028, '2015-09-26 04:43:00', 54),
    (12028, '2015-08-19 17:39:00', 47),
    (12028, '2015-04-08 17:36:00', 56),
    (12028, '2015-05-08 10:40:00', 45),
    (12028, '2015-05-20 01:53:00', 69),
    (12028, '2015-07-19 21:14:00', 51),
    (12597, '2015-09-16 21:54:00', 48),
    (12597, '2015-08-04 09:47:00', 51),
    (12597, '2015-01-02 16:46:00', 62),
    (12826, '2015-01-02 19:40:00', 42),
    (12826, '2015-06-21 19:28:00', 46),
    (12826, '2015-06-14 03:00:00', 60),
    (12826, '2015-07-18 23:27:00', 49),
    (12826, '2015-07-07 09:53:00', 57),
    (12826, '2015-06-04 20:20:00', 63),
    (12826, '2015-07-18 06:33:00', 48),
    (13014, '2015-08-07 17:16:00', 61),
    (13014, '2015-08-19 11:58:00', 63),
    (13014, '2015-01-02 19:43:00', 45),
    (13569, '2015-06-22 14:26:00', 23),
    (13569, '2015-06-11 02:11:00', 53),
    (13569, '2015-06-01 21:03:00', 42),
    (13569, '2015-06-03 15:21:00', 39),
    (13569, '2015-07-13 11:37:00', 67),
    (13569, '2015-01-02 20:58:00', 65),
    (13616, '2015-05-24 02:53:00', 46),
    (13616, '2015-01-02 21:07:00', 69),
    (13616, '2015-04-19 04:17:00', 60),
    (13616, '2015-06-02 14:52:00', 33),
    (13616, '2015-05-23 07:49:00', 57),
    (13616, '2015-04-06 13:43:00', 45),
    (15005, '2015-05-24 12:34:00', 63),
    (15005, '2015-01-02 22:29:00', 55),
    (15005, '2015-07-25 07:49:00', 33),
    (15005, '2015-05-04 05:41:00', 65),
    (15338, '2015-04-22 21:11:00', 36),
    (15338, '2015-04-20 18:11:00', 47),
    (15338, '2015-04-20 23:48:00', 56),
    (15338, '2015-08-21 06:31:00', 85),
    (15338, '2015-01-03 01:42:00', 48),
    (15338, '2015-06-14 15:31:00', 67),
    (15338, '2015-08-28 04:13:00', 71),
    (15338, '2015-04-22 14:20:00', 60),
    (15338, '2015-07-10 04:49:00', 46),
    (15768, '2015-01-03 01:57:00', 53),
    (15768, '2015-07-30 04:38:00', 47),
    (15768, '2015-04-14 14:08:00', 63),
    (15768, '2015-06-21 05:45:00', 31),
    (15768, '2015-09-14 04:28:00', 48),
    (15768, '2015-07-19 23:12:00', 50),
    (15768, '2015-07-18 01:59:00', 39),
    (15768, '2015-08-27 23:01:00', 50),
    (15822, '2015-01-03 04:35:00', 72),
    (15822, '2015-08-19 05:28:00', 64),
    (15822, '2015-05-04 07:17:00', 77),
    (15822, '2015-04-17 10:32:00', 29),
    (15822, '2015-05-23 06:07:00', 49),
    (15960, '2015-05-21 15:31:00', 71),
    (15960, '2015-01-03 04:58:00', 68),
    (15960, '2015-06-17 05:48:00', 45),
    (15960, '2015-04-07 23:16:00', 58),
    (16627, '2015-01-03 06:36:00', 74),
    (16627, '2015-07-28 04:36:00', 55),
    (16627, '2015-04-03 22:17:00', 54),
    (16627, '2015-04-27 14:58:00', 58),
    (16627, '2015-05-20 05:11:00', 44),
    (16627, '2015-06-03 15:58:00', 52),
    (16627, '2015-08-21 10:54:00', 63),
    (16627, '2015-08-03 18:37:00', 38),
    (17357, '2015-06-08 01:38:00', 60),
    (17357, '2015-01-03 07:40:00', 36),
    (17357, '2015-07-31 15:38:00', 32),
    (17357, '2015-08-30 01:44:00', 47),
    (17357, '2015-05-04 12:13:00', 59),
    (17357, '2015-06-08 10:37:00', 50),
    (17357, '2015-05-17 17:15:00', 45),
    (17357, '2015-09-09 12:31:00', 40),
    (17357, '2015-05-02 16:23:00', 48),
    (17357, '2015-04-14 13:51:00', 49),
    (17576, '2015-09-25 01:13:00', 34),
    (17576, '2015-01-03 09:10:00', 42),
    (17576, '2015-08-14 14:05:00', 48),
    (17576, '2015-09-19 16:40:00', 54),
    (17697, '2015-01-03 09:53:00', 22),
    (17697, '2015-08-03 11:10:00', 57),
    (17697, '2015-05-10 02:32:00', 35),
    (17697, '2015-07-01 20:12:00', 52),
    (17697, '2015-04-30 16:02:00', 32),
    (17697, '2015-09-25 23:41:00', 44),
    (19030, '2015-01-03 13:53:00', 55),
    (19030, '2015-07-12 20:29:00', 42),
    (19030, '2015-09-15 07:12:00', 56),
    (19030, '2015-07-15 03:07:00', 55),
    (19030, '2015-08-18 18:46:00', 46),
    (19030, '2015-05-07 11:59:00', 44),
    (19030, '2015-08-21 21:48:00', 36),
    (21582, '2015-01-03 14:16:00', 49),
    (21582, '2015-08-14 11:23:00', 52),
    (21582, '2015-08-19 16:55:00', 64),
    (21582, '2015-04-26 20:48:00', 46),
    (22376, '2015-09-24 00:47:00', 71),
    (22376, '2015-05-01 09:48:00', 51),
    (22376, '2015-09-11 08:12:00', 50),
    (22376, '2015-01-03 16:29:00', 65),
    (22376, '2015-08-02 14:13:00', 50),
    (22530, '2015-05-15 04:21:00', 33),
    (22530, '2015-07-12 10:16:00', 49),
    (22530, '2015-08-11 04:36:00', 50),
    (22530, '2015-06-30 07:14:00', 28),
    (22530, '2015-09-20 21:09:00', 58),
    (22530, '2015-06-13 06:58:00', 52),
    (22530, '2015-08-14 00:30:00', 41),
    (22530, '2015-06-22 21:13:00', 64),
    (22530, '2015-01-03 17:20:00', 39),
    (23027, '2015-04-16 20:00:00', 66),
    (23027, '2015-08-25 06:59:00', 32),
    (23027, '2015-09-06 23:32:00', 37),
    (23027, '2015-08-10 21:23:00', 52),
    (23027, '2015-09-09 02:11:00', 45),
    (23027, '2015-01-03 18:31:00', 55),
    (23410, '2015-09-17 14:33:00', 53),
    (23410, '2015-06-16 02:40:00', 50),
    (23410, '2015-05-14 15:28:00', 56),
    (23410, '2015-05-02 20:21:00', 60),
    (23410, '2015-09-14 16:50:00', 44),
    (23410, '2015-01-03 20:20:00', 56),
    (23410, '2015-06-20 09:54:00', 53),
    (23424, '2015-01-03 20:34:00', 47),
    (23424, '2015-06-25 00:39:00', 36),
    (23424, '2015-06-28 11:59:00', 37),
    (23424, '2015-07-06 15:14:00', 48),
    (23424, '2015-04-08 17:38:00', 45),
    (23424, '2015-06-05 05:45:00', 60),
    (23424, '2015-09-07 11:35:00', 79),
    (24027, '2015-08-04 14:32:00', 50),
    (24027, '2015-05-05 06:46:00', 40),
    (24027, '2015-08-25 16:19:00', 50),
    (24027, '2015-01-03 20:47:00', 60),
    (24069, '2015-05-17 04:21:00', 42),
    (24069, '2015-05-24 05:17:00', 50),
    (24069, '2015-04-04 13:58:00', 45),
    (24069, '2015-01-03 21:48:00', 46),
    (24069, '2015-07-02 17:53:00', 63),
    (24069, '2015-07-09 03:02:00', 47)
;

-- We have two tables. One is user id and their signup date. The other one shows all transactions done by those users, 
-- when the transaction happens and its corresponding dollar amount.

-- Find the average and median transaction amount only considering those transactions that happen on the same date as that user signed-up.

--------------- sol1 ----------------
/*
SELECT AVG(tot_trans) AS avg_trans, 
AVG(median_trans) AS median_trans
FROM (
SELECT a.user_id, ISNULL(tot_trans,0) AS tot_trans, PERCENTILE_DISC(0.5) WITHIN GROUP(ORDER BY ISNULL(tot_trans,0)) OVER() AS median_trans
FROM users AS a LEFT JOIN 
(SELECT user_id, transaction_date, SUM(transaction_amount) AS tot_trans
 FROM transactions 
 GROUP BY user_id, transaction_date) AS b 
ON a.user_id = b.user_id AND a.sign_up_date = CONVERT(date, b.transaction_date)
) AS t

*/
--------------- sol2 ----------------
WITH t AS (
SELECT a.user_id, ISNULL(tot_trans,0) AS tot_trans, ROW_NUMBER() OVER(ORDER BY ISNULL(tot_trans,0)) AS rank_trans
FROM users AS a LEFT JOIN 
(SELECT user_id, transaction_date, SUM(transaction_amount) AS tot_trans
 FROM transactions 
 GROUP BY user_id, transaction_date) AS b 
ON a.user_id = b.user_id AND a.sign_up_date = CONVERT(date, b.transaction_date)
),
rn AS (SELECT (COUNT(*)+1)/2 AS k
       FROM t
       UNION ALL
       SELECT (COUNT(*)+2)/2 --- directly takes floor
       FROM t)

SELECT *
FROM
(SELECT tot_trans AS median_trans
 FROM t
 WHERE rank_trans IN (SELECT * FROM rn)) a CROSS JOIN
(SELECT AVG(tot_trans) AS avg_trans FROM t) b

View schema
Execution time: 0,26 sec, rows selected: 1, rows affected: 1062, absolute service time: 0,44 sec, absolute service time: 0,45 sec