window function Task 1 completed

aharlamcev/postgresql/WindowFunctionHomework.sql

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+create table products_extended (
+id INT primary key, 
+name VARCHAR(50) not null,
+category VARCHAR(50) not null,
+price INT,
+in_stock BOOLEAN default true,
+email_support VARCHAR(50)
+);
+
+insert into products_extended (id, name, category, price, in_stock, email_support)
+values (1, 'iPhone 14', 'smartphone', 799, true, 'iphone@apple.com'),
+(2, 'MacBook Air', 'laptop', 1199,	false,	NULL),
+(3, 'Galaxy S22', 'smartphone',	699,	true,	'galaxy@support.com'),
+(4, 'ThinkPad X1',	'laptop',	1399,	true,	'thinkpad@lenovo.com'),
+(5, 'iPad Pro',	'tablet',	999,	false,	'ipad@apple.com'),
+(6, 'Kindle Paperwhite',	'ebook_reader',	149,	true,	NULL),
+(7, 'Mi Band 7',	'smartwatch',	49,	true,	'miband@xiaomi.com'),
+(8, 'Surface Pro',	'tablet',	1299,	true,	'surface@microsoft.com'),
+(9, 'Honor Pad X9',	'tablet',	219,	true,	'honor@support.com'),
+(10, 'Dell XPS 13',	'laptop',	1099,	false,	'dell@support.com');
+
+select * from products_extended
+
+with email_false as (select * from 
+(
+select category, name, price, email_support, row_number() over (partition by category order by price desc) as rn
+from products_extended where email_support is null)
+),
+
+email_true as (select * from 
+(
+select category, name, price, email_support, row_number() over (partition by category order by price desc) as rn
+from products_extended where email_support is not null) where rn = 1
+)
+
+select category, name, price, email_support from email_false
+union all
+select category, name, price, email_support from email_true
+order by category, price desc