MySQL列转行、行转列

1795. 每个产品在不同商店的价格

列转行

SELECT product_id, 'store1' store, store1 price FROM products WHERE store1 IS NOT NULL
UNION
SELECT product_id, 'store2' store, store2 price FROM products WHERE store2 IS NOT NULL
UNION
SELECT product_id, 'store3' store, store3 price FROM products WHERE store3 IS NOT NULL;

行转列

SELECT 
  product_id,
  SUM(IF(store = 'store1', price, NULL)) 'store1',
  SUM(IF(store = 'store2', price, NULL)) 'store2',
  SUM(IF(store = 'store3', price, NULL)) 'store3' 
FROM
  Products1 
GROUP BY product_id ;