First commit

Week3/Solutions/hw2_task1.sql

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+select a.title as album_name
+from album as a
+   join track as t
+      on a.album_id=t.album_id
+   where t.milliseconds > 250000
+   group by a.title;
+
+
+select a.title as album_name, count(t) as cnt
+from album as a
+   join track as t
+      on a.album_id = t.album_id
+   group by a.title;

Week3/Solutions/hw2_task10.sql

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+with sum_track as (
+               select album.title as album_name,album.artist_id, count(t.track_id) as count_t, m_t.name
+        from album
+        join track t on album.album_id = t.album_id
+        join media_type as m_t on t.media_type_id = m_t.media_type_id
+        --join invoice_line il on t.track_id = il.track_id
+        group by album.title, album.artist_id, m_t.name
+        order by album.title
+    ),
+     q1 as (
+    select sum_track.album_name, max(sum_track.count_t) as cnt
+    from sum_track
+    group by sum_track.album_name
+),
+     q2 as(
+         select sum_track.artist_id,sum_track.name, count(sum_track.album_name) as c_1
+         from sum_track
+         join q1 on sum_track.album_name=q1.album_name
+         where sum_track.count_t=q1.cnt
+         group by sum_track.artist_id, sum_track.name
+         order by  sum_track.artist_id,  sum_track.name     ),
+     q3 as(
+         select q2.artist_id, max(q2.c_1) as m_c
+         from q2
+         group by q2.artist_id
+     ),
+    q4 as(
+        select q2.artist_id, count(q2.name) as all_album
+        from q2
+        group by q2.artist_id
+        order by q2.artist_id
+      )
+     ,
+     q5 as (
+         select a.name as artist_name, q2.name as media_type_name, q3.m_c as media_cnt, q4.all_album aswhole_cnt
+         from artist as a
+         join q4 on a.artist_id=q4.artist_id
+         join q3 on a.artist_id=q3.artist_id
+         join q2 on q3.artist_id=q2.artist_id
+         where q2.c_1=q3.m_c
+         )
+select *
+from q5;

Week3/Solutions/hw2_task2.sql

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+select g.name as general_name, mt.name as media_type, count(t) as cnt
+from track as t
+   join genre as g
+      on g.genre_id = t.genre_id
+   join media_type mt
+      on t.media_type_id = mt.media_type_id
+   group by g.name, mt.name

Week3/Solutions/hw2_task3.sql

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+select concat(emp.first_name,' ', emp.last_name) as employee_full_name, emp.birth_date as employee_birth_date,
+       emp.hire_date as employee_hire_date, concat(manager.first_name, ' ', manager.last_name) as manager_full_name,
+       manager.birth_date as manager_birth_date, manager.hire_date as manager_hire_date
+from employee as emp
+    left
+   join employee as manager
+      on emp.reports_to = manager.employee_id
+   where emp.birth_date < manager.birth_date
+   and emp.hire_date > manager.hire_date;
+

Week3/Solutions/hw2_task4.sql

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+select art.name as artist_name, count(tr) as qty
+from track as tr
+join genre g on tr.genre_id = g.genre_id
+join album a on tr.album_id = a.album_id
+join artist art on a.artist_id = art.artist_id
+where g.name in ('Rock', 'Metal')
+group by art.artist_id

Week3/Solutions/hw2_task5.sql

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+select concat(emp.first_name,' ', emp.last_name) as employee_full_name, count(distinct i) as invoices_count,
+       count(distinct c) customers_count, count(distinct i.billing_address) as addresses_count,
+       count(i_l.track_id) as tracks_count
+from employee as emp
+join customer c on emp.employee_id = c.support_rep_id
+join invoice as i on c.customer_id = i.customer_id
+join invoice_line i_l on i.invoice_id = i_l.invoice_id
+group by emp.employee_id;
+

Week3/Solutions/hw2_task6.sql

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+-- select  c.last_name
+--    from customer as c
+--    order by length(c.last_name)-length(replace(lower(c.last_name),'a', ''));
+-- -- select *
+-- -- from customer;
+--
+--
+-- select length(c.last_name)-length(replace(lower(c.last_name),'a', '')) as s
+--    from customer as c
+--    group by s
+--    order by s;
+
+select  CASE
+   when length(c.last_name)-length(replace(lower(c.last_name),'a', '')) = 0
+      then 'A'
+   when length(c.last_name)-length(replace(lower(c.last_name),'a', '')) = 1
+      then 'B'
+   when length(c.last_name)-length(replace(lower(c.last_name),'a', '')) = 2
+      then 'C'
+   else 'D'
+  END segment_group, count(distinct mt)
+   from customer as c
+   join invoice i on c.customer_id = i.customer_id
+   join invoice_line i_C on i.invoice_id = i_c.invoice_id
+   join track t on i_C.track_id = t.track_id
+   join media_type mt on t.media_type_id = mt.media_type_id
+   join genre g on g.genre_id = t.genre_id
+   where g.name in ('Metal', 'Heavy Metal')
+   group by segment_group
+   order by segment_group;

Week3/Solutions/hw2_task7.sql

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+     --Жанр - компания - песня - кол-во покупок
+   with  gen_comp_track as(
+     select g.name, c.company, t.name as t_name, il.quantity
+    from genre as g
+    join track t on g.genre_id = t.genre_id
+    join invoice_line il on t.track_id = il.track_id
+    join invoice i on i.invoice_id = il.invoice_id
+    join customer c on c.customer_id = i.customer_id
+    where c.company is not null
+    group by g.name, c.company, t.name, il.quantity
+    order by g.name, c.company, il.quantity
+    )
+     --Жанр и количество покупок одной компанией
+     ,
+     q2 as(
+         select gen_comp_track.name, gen_comp_track.company, count(company) as count
+         from gen_comp_track
+         group by gen_comp_track.name, gen_comp_track.company
+         order by gen_comp_track.name
+
+     )
+     -- жанр - максмальная покупка
+     ,
+     q3 as(
+            select q2.name, max(count) as max_count
+            from q2
+            group by q2.name
+            order by q2.name
+
+     )
+     -- жанр - компания, которая больше купила этот жанр(соеденияем q2 и q3)
+,
+     q4 as(
+            select distinct on(q3.name) q3.name, q2.company, gen_comp_track.t_name,q3.max_count
+            from q2
+            join gen_comp_track on q2.name=gen_comp_track.name
+            join q3 on q3.name = q2.name
+            where q2.count = q3.max_count
+
+          )
+
+select q4.company as company_name, q4.t_name as track_name
+from q4;
+

Week3/Solutions/hw2_task8.sql

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+
+-- в выборе убираются песни, которые не были куплены ни разу
+--жанры - трек - кол-во покупок
+with popular as (
+    select  g.name as g_name, t.name as t_name, sum(il.quantity) as quan
+    from genre as g
+    join track t on g.genre_id = t.genre_id
+    join invoice_line il on t.track_id = il.track_id
+    group by g.name, il.quantity, t.name
+    order by g.name,il.quantity, t.name
+),
+-- жанр - кол-во песен, которые покупали более одного раза
+     q1 as (
+         select popular.g_name as name, count(popular.quan) as cnt
+         from popular
+         group by popular.g_name
+-- жанр-трек-процент покупки песни от q1
+     ),
+     q2 as(
+         select popular.g_name, popular.t_name,
+                round((popular.quan::numeric/q1.cnt::numeric)*100, 2) as round_q2
+         from popular
+         join q1 on q1.name=popular.g_name
+         order by popular.g_name, round_q2 desc , popular.t_name
+
+     ),
+     -- q2 и индексация
+     q3 as(
+      select *, rank() over(partition by q2.g_name order by q2.round_q2 desc, q2.t_name) as indc
+         from q2
+         order by q2.g_name, q2.round_q2 desc , q2.t_name
+     ),
+     -- жанр-трек-процент с учетом предыдущего
+     q4 as (
+         select q3_s.g_name, q3_s.t_name, sum(q3_f.round_q2) as percent
+         from q3 as q3_f
+         join q3 as q3_s on q3_f.g_name=q3_s.g_name
+         and q3_f.indc <= q3_s.indc
+         group by q3_s.g_name, q3_s.t_name, q3_s.indc
+         order by q3_s.g_name, q3_s.indc
+     ),
+     -- q4 только треки, входящие в 25% популярных
+     q5 as(
+         select q4.g_name,q4.t_name
+         from q4
+         where q4.percent <= 25
+     )
+-- конечный вывод
+select q5.t_name as track_name, q2.round_q2 as popularity
+         from q5
+         join q2 on q5.g_name=q2.g_name and q5.t_name=q2.t_name
+
+
+
+
+

Week3/Solutions/hw2_task9.sql

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+
+-- Подсчет суммы миллисекунд одинакого жанра
+with sum_track as (
+               select album.title as album_name, sum(t.milliseconds) as track_mil,sum(il.quantity) as track_buy, g.name as genre_name
+        from album
+        join track t on album.album_id = t.album_id
+        join genre g on t.genre_id = g.genre_id
+        join invoice_line il on t.track_id = il.track_id
+        group by album.title, g.name
+        order by album.title
+    ),
+     q1 as (
+    select sum_track.album_name, max(sum_track.track_mil) as cnt
+    from sum_track
+    group by sum_track.album_name
+)
+select q1.album_name, sum_track.genre_name, q1.cnt
+from q1
+join sum_track on sum_track.album_name=q1.album_name
+where q1.cnt = sum_track.track_mil
+group by q1.album_name, sum_track.genre_name, q1.cnt;