Jak uniknąć duplikatów pisząc subquery w select.

USE Electrionics
SELECT 
	item_id,
	price,
	(SELECT AVG(price) FROM items) AS avg_price,
	price - (SELECT AVG(price) FROM items) as avg_difference
FROM items

USE Electrionics
SELECT 
	item_id,
	price,
	(SELECT AVG(price) FROM items) AS avg_price,
	price - (SELECT avg_price) as avg_difference
FROM items

WITH Something
AS (
  SELECT 
      item_id,
      price,
      (SELECT AVG(price) FROM items) AS avg_price
  FROM items
)
SELECT
  item_id,
  price,
  avg_prive,
  price - avg_price AS avg_difference
FROM Something

SELECT 
    item_id,
    price,
    avg_price,
    price - avg_price as avg_difference
FROM items
cross join  (SELECT AVG(price) avg_price FROM items)  a