added solution for Week3

Week3/solutions/hw2_task1.sql

@@ -0,0 +1,8 @@
+select a.title  as album_name,
+       count(*) as cnt
+  from track t
+  join album a
+    on t.album_id = a.album_id
+ group
+    by a.album_id
+having (avg(t.milliseconds) > 250000);

Week3/solutions/hw2_task10.sql

@@ -0,0 +1,83 @@
+with t1 as (
+    select a.album_id   as album_id,
+           a.title      as album_name,
+           mt.name      as mt_name,
+           sum(t.bytes) as size_per_mt,
+           a.artist_id  as artist_id
+    from album a
+             join track t
+                  on a.album_id = t.album_id
+             join media_type mt
+                  on t.media_type_id = mt.media_type_id
+    group by a.album_id, a.title, mt.name
+),
+     t2 as (
+         select t1.album_id         as album_id,
+                t1.artist_id        as artist_id,
+                max(t1.size_per_mt) as max_size
+         from t1
+         group by t1.album_id, t1.artist_id
+     ),
+     t3 as (
+         select t1.album_id   as album_id,
+                t1.album_name as album_name,
+                t1.mt_name    as mt_name,
+                t1.artist_id  as artist_id
+         from t2
+                  join t1
+                       on (t2.album_id, t2.max_size) = (t1.album_id, t1.size_per_mt)
+     ),
+     t4 as (
+         select ar.artist_id as artist_id,
+                ar.name      as artist_name,
+                t3.mt_name   as mt_name
+         from artist ar
+                  left join t3
+                            on ar.artist_id = t3.artist_id
+     ),
+     t5 as (
+         select t4.artist_id   as artist_id,
+                t4.artist_name as artist_name,
+                count(*)       as whole_cnt
+         from t4
+         group by t4.artist_id, t4.artist_name
+     ),
+     t6 as (
+         select t4.artist_id   as artist_id,
+                t4.artist_name as artist_name,
+                t4.mt_name     as mt_name,
+                count(*)       as media_cnt
+         from t4
+         group by t4.artist_id, t4.artist_name, t4.mt_name
+     ),
+     t7 as (
+         select t6.artist_id      as artist_id,
+                t6.artist_name    as artist_name,
+                max(t6.media_cnt) as media_cnt
+         from t6
+         group by t6.artist_id, t6.artist_name
+     ),
+     t8 as (
+         select distinct on (t6.mt_name, t6.artist_id) t6.mt_name     as mt_name,
+                                                       t6.artist_id   as artist_id,
+                                                       t6.artist_name as artist_name
+         from t6
+                  join t7
+                       on (t7.artist_id, t7.media_cnt) = (t6.artist_id, t6.media_cnt)
+         order by t6.mt_name, t6.artist_id
+     )
+select t8.artist_name as artist_name,
+       t8.mt_name     as media_type_name,
+       CASE
+           when (t8.mt_name is null) then 0
+           else t7.media_cnt
+           end        as media_cnt,
+       CASE
+           when (t8.mt_name is null) then 0
+           else t5.whole_cnt
+           end        as whole_cnt
+from t8
+         join t7
+              on t7.artist_id = t8.artist_id
+         join t5
+              on t5.artist_id = t8.artist_id;

Week3/solutions/hw2_task2.sql

@@ -0,0 +1,10 @@
+select g.name   as g_name,
+       mt.name  as mt_name,
+       count(*) as cnt
+  from track t
+  join genre g
+    on g.genre_id = t.genre_id
+  join media_type mt
+    on mt.media_type_id = t.media_type_id
+ group
+    by (g.genre_id, mt.media_type_id);

Week3/solutions/hw2_task3.sql

@@ -0,0 +1,12 @@
+select e1.last_name || ' ' || e1.first_name as emp_full_name,
+       e1.birth_date                        as emp_birth_date,
+       e1.hire_date                         as epm_hire_date,
+       e2.last_name || ' ' || e2.first_name as manager_full_name,
+       e2.birth_date                        as manager_birth_date,
+       e2.hire_date                         as manager_hire_date
+  from employee e1
+ inner
+  join employee e2
+    on e1.reports_to = e2.employee_id
+ where (e1.birth_date < e2.birth_date)
+   and (e1.hire_date > e2.hire_date);

Week3/solutions/hw2_task4.sql

@@ -0,0 +1,19 @@
+with artists_id_and_count as
+(
+           select a.artist_id as ar_id,
+                  count(*)    as cnt
+             from track t
+             join album a
+               on a.album_id = t.album_id
+            where t.genre_id in (
+               select genre_id
+               from genre
+               where name in ('Rock', 'Metal')
+           )
+           group by a.artist_id
+)
+select art.name as artist_name,
+       c.cnt    as qty
+  from artist art
+  join artists_id_and_count c
+    on c.ar_id = art.artist_id;

Week3/solutions/hw2_task5.sql

@@ -0,0 +1,14 @@
+select e.last_name || ' ' || e.first_name as empl_full_name,
+       count(distinct c.customer_id)      as customer_cnt,
+       count(distinct i.invoice_id)       as invoice_cnt,
+       count(distinct i.billing_address)  as addresses_cnt,
+       sum(i_l.quantity)                  as tracks_cnt
+  from customer c
+  join employee e
+    on c.support_rep_id = e.employee_id
+  join invoice i
+    on c.customer_id = i.customer_id
+  join invoice_line i_l
+    on i.invoice_id = i_l.invoice_id
+ group
+    by e.employee_id;

Week3/solutions/hw2_task6.sql

@@ -0,0 +1,21 @@
+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'
+           when (length(c.last_name) - length(REPLACE(lower(c.last_name), 'a', '')) >= 3) then 'D'
+           end                 as segment_group,
+       count(distinct mt.name) as cnt
+  from customer c
+  join invoice i
+    on c.customer_id = i.customer_id
+  join invoice_line i_l
+    on i.invoice_id = i_l.invoice_id
+  join track t
+    on i_l.track_id = t.track_id
+  join genre g
+    on t.genre_id = g.genre_id
+  join media_type mt
+    on mt.media_type_id = t.media_type_id
+ where  lower(g.name) like '%metal%'
+ group
+    by segment_group;

Week3/solutions/hw2_task7.sql

@@ -0,0 +1,50 @@
+with t1 as (
+    select g.name            as g_name,
+           c.company         as company_name,
+           sum(i_l.quantity) as tracks_per_comp_and_genre,
+           t.name            as track_name
+    from customer c
+             join invoice i
+                  on c.customer_id = i.customer_id
+             join invoice_line i_l
+                  on i.invoice_id = i_l.invoice_id
+             join track t
+                  on i_l.track_id = t.track_id
+             join genre g
+                  on t.genre_id = g.genre_id
+    where company is not null
+    group by g.name, c.company, t.track_id
+), t2 as (
+    select t1.g_name                         as g_name,
+           t1.company_name                   as company_name,
+           sum(t1.tracks_per_comp_and_genre) as sum_tracks
+    from t1
+    group by t1.g_name, t1.company_name
+), t3 as (
+    select t2.g_name          as g_name,
+           max(t2.sum_tracks) as max_per_genre
+    from t2
+    group by t2.g_name
+), t4 as (
+    select distinct on (t2.g_name) t2.g_name, t2.company_name
+    from t2
+    join t3
+      on (t2.g_name, t2.sum_tracks) = (t3.g_name, t3.max_per_genre)
+   order
+      by t2.g_name, t2.company_name
+), t5 as (
+    select t1.g_name,
+           t1.company_name,
+           t1.tracks_per_comp_and_genre
+     from t4
+     join t1
+       on (t1.g_name, t1.company_name) = (t4.g_name, t4.company_name)
+)
+select res.company_name, res.track_name
+  from (
+           select distinct on (t1.g_name) t1.g_name, t1.company_name, t1.track_name
+           from t1
+           where (t1.g_name, t1.company_name, t1.tracks_per_comp_and_genre)
+                     in (select * from t5)
+           order by t1.g_name, t1.track_name
+       ) as res;

Week3/solutions/hw2_task8.sql

@@ -0,0 +1,43 @@
+with t1 as (
+    select t.track_id as track_id,
+           t.name as track_name,
+           g.name as genre_name,
+           sum(il.quantity) as purchases_of_track
+    from track t
+             join genre g
+                  on t.genre_id = g.genre_id
+             join invoice_line il
+                  on t.track_id = il.track_id
+    group by t.track_id, t.name, g.name
+), t2 as (
+    select t1.genre_name as genre_name,
+           sum(t1.purchases_of_track) as sum_per_genre
+      from t1
+     group
+        by t1.genre_name
+), t3 as (
+    select t1.genre_name                                                                        as genre_name,
+           t1.track_id                                                                          as track_id,
+           t1.track_name                                                                        as track_name,
+           t1.purchases_of_track / t2.sum_per_genre * 100                                       as popularity,
+           row_number() over (partition by t1.genre_name order by t1.genre_name, t1.track_name) as num
+    from t1
+             join t2
+                  on t1.genre_name = t2.genre_name
+    order by t1.genre_name, t1.track_name
+), t4 as (
+    select cp1.genre_name,
+           cp1.track_id        as track_id,
+           cp1.track_name      as track_name,
+           sum(cp2.popularity) as gap
+    from t3 cp1
+             join t3 cp2
+                  on cp1.genre_name = cp2.genre_name and cp1.num >= cp2.num
+    group by cp1.track_id, cp1.track_name, cp1.genre_name
+)
+select t4.track_name as track_name,
+       t3.popularity as popularity
+  from t4
+  join t3
+    on t3.track_id = t4.track_id
+ where t4.gap <= 25;

Week3/solutions/hw2_task9.sql

@@ -0,0 +1,49 @@
+with t1 as (
+    select a.album_id     as album_id,
+           a.title        as album_title,
+           t.milliseconds as track_duration,
+           g.name         as genre_name
+    from album a
+             join track t
+                  on a.album_id = t.album_id
+             join genre g
+                  on t.genre_id = g.genre_id
+), t2 as (
+    select t1.album_id            as album_id,
+           t1.album_title         as album_title,
+           t1.genre_name          as genre_name,
+           sum(t1.track_duration) as duration_per_genre
+    from t1
+    group by t1.album_id, t1.album_title, t1.genre_name
+), t3 as (
+    select t2.album_id                as album_id,
+           t2.album_title             as album_title,
+           max(t2.duration_per_genre) as max_duration
+    from t2
+    group by t2.album_id, t2.album_title
+), t4 as (
+    select t3.album_id    as album_id,
+           t3.album_title as album_title,
+           t2.genre_name  as genre_name
+    from t3
+             join t2
+                  on (t3.album_id, t3.max_duration) =
+                     (t2.album_id, t2.duration_per_genre)
+), t5 as (
+    select a.album_id       as album_id,
+           a.title          as album_title,
+           sum(il.quantity) as cnt
+    from album a
+             join track t
+                  on a.album_id = t.album_id
+             join invoice_line il
+                  on t.track_id = il.track_id
+    group by a.album_id, a.title
+)
+select t4.album_title      as album_name,
+       t4.genre_name       as genre_name,
+       coalesce(t5.cnt, 0) as cnt
+  from t4
+  left
+  join t5
+    on t5.album_id = t4.album_id;

Week4/solutions/hw4_task1.sql

@@ -0,0 +1,13 @@
+select distinct on (art.artist_id, g.name) art.name       as artist_name,
+                                           g.name         as genre_name,
+                                           t.name         as track_name,
+                                           t.milliseconds as track_length
+  from artist art
+  join album a
+    on art.artist_id = a.artist_id
+  join track t
+    on a.album_id = t.album_id
+  join genre g
+    on t.genre_id = g.genre_id
+ order
+    by art.artist_id, g.name, t.milliseconds desc;

Week4/solutions/hw4_task2.sql

@@ -0,0 +1,24 @@
+with t1 as (select c.company                   as company_name,
+                   t.name                      as track_name,
+                   g.name                      as genre_name,
+                   a.title                     as album_name,
+                   il.quantity * il.unit_price as price
+            from customer c
+                     join invoice i
+                          on c.customer_id = i.customer_id
+                     join invoice_line il
+                          on i.invoice_id = il.invoice_id
+                     join track t
+                          on il.track_id = t.track_id
+                     join genre g
+                          on t.genre_id = g.genre_id
+                     join album a
+                          on t.album_id = a.album_id
+            where c.company is not null
+)
+select distinct on (t1.company_name) t1.company_name as company_name,
+                                     t1.track_name   as track_name,
+                                     t1.genre_name   as genre_name,
+                                     t1.album_name   as album_name
+from t1
+order by t1.company_name, t1.price desc, t1.track_name;

Week4/solutions/hw4_task3.sql

@@ -0,0 +1,28 @@
+with t1 as (select distinct on (hire_date)
+                   hire_date                    as hire_date,
+                   coalesce(
+                             lag(hire_date) over (order by hire_date),
+                             to_timestamp('1998-12-31', 'YYYY-MM-DD')
+                           )                    as previous_date
+            from employee
+            order by hire_date
+), t2 as (
+    select t1.hire_date     as hire_date,
+           t1.previous_date as previous_date
+    from t1
+    where t1.hire_date - t1.previous_date > '1 day'
+), t3 as (
+    select t2.hire_date     as hire_date,
+           t2.previous_date as previous_date,
+           coalesce(
+                      lead(t2.hire_date) over (order by t2.hire_date),
+                      to_timestamp('2020-01-02', 'YYYY-MM-DD')
+                   )        as next_date
+    from t2
+)
+select coalesce(t_1.previous_date, t_2.hire_date) + interval '1 day' as date_start,
+       coalesce(t_1.hire_date, t_2.next_date) - interval '1 day'     as date_end
+  from t3 t_1
+  full
+  join t3 t_2
+    on t_1.hire_date = t_2.next_date;