дз 3

hws/hw_3.sql

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+--Задание 1. Использование операторов наборов записей (UNION, EXCEPT, INTERSECT)
+--1.	Выведите 2 самых первых заказа сделанных первым заказчиком (custid=1) и 2 самых последних его заказа. Выборка должна быть упорядочена по годам и месяцам 
+(select btrim(split_part(c.companyname,' ',2)), orderid , to_char(orderdate, 'MM-YYYY') AS "month-year"
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on o.custid=c.custid
+where c.custid=1 
+order by o.orderdate asc
+limit 2 )
+union
+(select btrim(split_part(c.companyname,' ',2)), orderid , to_char(orderdate, 'MM-YYYY') AS "month-year"
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on o.custid=c.custid
+where c.custid=1 
+order by o.orderdate desc
+limit 2 )
+order by orderid;
+--2.	Выведите по 2 самых дешевых продукта каждого поставщика из списка (2, 5, 15, 25). 
+--Выборка должна быть упорядочена по категории и цене.
+((select btrim(split_part(companyname, ' ',2)), productname, unitprice,categoryname
+from "Production"."Suppliers" as s
+join "Production"."Products" as p on p.supplierid=s.supplierid
+join "Production"."Categories" as c on p.categoryid=c.categoryid
+where s.supplierid = 2
+order by p.unitprice
+limit 2)
+union all
+(select btrim(split_part(companyname, ' ',2)), productname, unitprice,categoryname
+from "Production"."Suppliers" as s
+join "Production"."Products" as p on p.supplierid=s.supplierid
+join "Production"."Categories" as c on p.categoryid=c.categoryid
+where s.supplierid = 5
+order by p.unitprice
+limit 2)
+union all
+(select btrim(split_part(companyname, ' ',2)), productname, unitprice,categoryname
+from "Production"."Suppliers" as s
+join "Production"."Products" as p on p.supplierid=s.supplierid
+join "Production"."Categories" as c on p.categoryid=c.categoryid
+where s.supplierid = 15
+order by p.unitprice
+limit 2)
+union all
+(select btrim(split_part(companyname, ' ',2)), productname, unitprice,categoryname
+from "Production"."Suppliers" as s
+join "Production"."Products" as p on p.supplierid=s.supplierid
+join "Production"."Categories" as c on p.categoryid=c.categoryid
+where s.supplierid = 25
+order by p.unitprice
+limit 2))
+order by categoryname asc, unitprice desc;
+--3.	Сформируйте 2 выборки следующего вида:
+--a.	В первом случае, выборка должна содержать список продуктов, которые входили в «корзину» 
+--первого покупателя (custid=1) и точно не входили в объединенные корзины 2 и 3 покупателей
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=1)
+except
+((select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=2)
+union all
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=3))
+--b.	Во втором случае, выборка должна включать только те продукты, которые присутствуют в 
+--продуктовых «корзинах» покупателей 2, 3 и 14 
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=2)
+intersect
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=3)
+intersect
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=14)
+--4.	Сформируйте 2 выборки следующего вида:
+--
+--a.	В первом случае выборка должна включать уникальный список только тех клиентов, с которыми 
+--сотрудник взаимодействовал в 2008 году и точно не взаимодействовал в 2007
+(select distinct o.empid, o.custid
+from "HR"."Employees" as e
+join "Sales"."Orders" as o on o.empid=e.empid 
+join "Sales"."Customers" as c on c.custid = o.custid 
+where orderdate between '2008-01-01' and '2008-12-31')
+except
+(select distinct o.empid, o.custid
+from "HR"."Employees" as e
+join "Sales"."Orders" as o on o.empid=e.empid 
+join "Sales"."Customers" as c on c.custid = o.custid 
+where orderdate between '2007-01-01' and '2007-12-31')
+--b.	Вторая выборка должна включать уникальный список тех клиентов, с которыми сотрудник взаимодействовал и в 2008 году и в 2007
+(select distinct o.empid, o.custid
+from "HR"."Employees" as e
+join "Sales"."Orders" as o on o.empid=e.empid 
+join "Sales"."Customers" as c on c.custid = o.custid 
+where orderdate between '2008-01-01' and '2008-12-31')
+intersect
+(select distinct o.empid, o.custid
+from "HR"."Employees" as e
+join "Sales"."Orders" as o on o.empid=e.empid 
+join "Sales"."Customers" as c on c.custid = o.custid 
+where orderdate between '2007-01-01' and '2007-12-31')
+--Задание 2. Анализ планов выполнения
+--1.	Проанализируйте план выполнения запроса из задания 1.3a
+explain analyze (select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=1)
+except
+((select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=2)
+union all
+(select productname,p.unitprice, categoryname
+from "Sales"."Customers" as c
+join "Sales"."Orders" as o on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=3))
+--Planning Time: 1.324 ms
+--2.	Измените порядок таблиц в предложении FROM и сравните планы выполнения. 
+explain analyze (select productname,p.unitprice, categoryname
+from "Sales"."Orders" as o
+join "Sales"."Customers" as c on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=1)
+except
+((select productname,p.unitprice, categoryname
+from "Sales"."Orders" as o
+join "Sales"."Customers" as c on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=2)
+union all
+(select productname,p.unitprice, categoryname
+from "Sales"."Orders" as o 
+join "Sales"."Customers" as c on c.custid=o.custid
+join "Sales"."OrderDetails" as od on od.orderid=o.orderid
+join "Production"."Products" as p on p.productid=od.productid
+join "Production"."Categories" as cat on cat.categoryid = p.categoryid 
+where c.custid=3))
+--Planning Time: 1.608 ms
+--3.	Определите, влияет ли порядок таблиц на производительность запроса.
+--Порядок таблиц в FROM влияет в основном на процесс планирования, так как оптимизатор рассматривает разные комбинации соединений.
+--4.	Приведите пример, объясните результат
+explain analyze
+select *
+from "Production"."Categories" as c
+join "Production"."Products" p on c.categoryid = p.categoryid;
+--Planning Time: 0.161 ms
+--Execution Time: 0.092 ms
+explain analyze
+select *
+from "Production"."Products" p
+join "Production"."Categories" c on c.categoryid = p.categoryid;
+--Planning Time: 0.138 ms
+--Execution Time: 0.081 ms
+--Вывод: Порядок таблиц в предложении FROM влияет на время построения плана (Planning Time), так как 
+--оптимизатор рассматривает разные комбинации соединений. Однако на фактическое время выполнения 
+--(Execution Time) порядок таблиц практически не влияет, так как PostgreSQL выбирает наиболее эффективный
+-- план независимо от исходного порядка таблиц.