如何從另一個MySQL減去一行

Question

鑒於附表

如何找到每天出售的Mac和Windows之間的區別。 有人可以解釋一下邏輯嗎

Answer 1

內部聯接將完成這項工作。

SELECT 
WindowsTable.Date,
ABS(WindowsTable.Sold - MacTable.Sold) absoluteDifference 
FROM
(SELECT 
*
FROM producttable
WHERE Products = 'Windows') WindowsTable

INNER JOIN 

(
SELECT 
*
FROM producttable
WHERE Products = 'Mac' ) MacTable

ON WindowsTable.Date = MacTable.Date;

此處演示

Answer 2

嘗試在日期使用INNER JOIN重塑查詢：

SELECT macs_sales.Date, (MacsSold - WindowsSold) AS sales_difference
FROM
(
  SELECT Date, Sold as MacsSold
  FROM computer_sales
  WHERE Products="Mac"
) macs_sales
INNER JOIN
(
  SELECT Date, Sold as WindowsSold
  FROM computer_sales
  WHERE Products="Windows"
) windows_sales
ON macs_sales.Date = windows_sales.Date