mysql - 如何使用两列得到第三列的结果

Question

我有这个 SQL 查询

SELECT
  SERVERPROPERTY('MachineName') AS FoodServer,
  SUM(Extended * Multiplier) AS GrossSale,
  (SELECT
    COUNT(*)
  FROM FinishedTransaction)
  AS counts
FROM finishedsales fs
LEFT JOIN FinishedTransaction ft
  ON fs.TransactionNo = ft.TransactionNo

现在，我想获取 GrossSale 列和计数列的商并将其显示到第三列。我在下面尝试了这个查询，但它不起作用。

SELECT
  SERVERPROPERTY('MachineName') AS FoodServer,
  SUM(Extended * Multiplier) AS GrossSale,
  (SELECT
    COUNT(*)
  FROM FinishedTransaction)
  AS counts,
  (GrossSale / counts) AS result
FROM finishedsales fs
LEFT JOIN FinishedTransaction ft
  ON fs.TransactionNo = ft.TransactionNo

这个替代解决方案正在工作..

SELECT
  SERVERPROPERTY('MachineName') AS FoodServer,
  SUM(Extended * Multiplier) AS GrossSale,
  (SELECT
    COUNT(*)
  FROM FinishedTransaction)
  AS counts,
  SUM(Extended * Multiplier) / (SELECT
    COUNT(*)
  FROM FinishedTransaction)
  AS result
FROM finishedsales fs
LEFT JOIN FinishedTransaction ft
  ON fs.TransactionNo = ft.TransactionNo

但我不想要那个解决方案，因为它有点冗长，而且性能不佳。我想知道该问题的最佳解决方案

Answer 1

我没有发现您的解决方案有任何问题，您可能更喜欢这个，但我怀疑您会获得更好的性能。

Select Foodserver, GrossSale, Counts, (GrossSale / counts) as result    
    FROM
    (
        SELECT SERVERPROPERTY ('MachineName') as FoodServer,
        SUM(Extended * Multiplier) as GrossSale, 
        (SELECT COUNT(*) FROM FinishedTransaction) as counts

        FROM finishedsales fs LEFT JOIN FinishedTransaction ft
        ON fs.TransactionNo = ft.TransactionNo
    ) as salesData

注意。你也应该在这里添加除以零检查..我认为where GrossSale <>0 AND Counts <>0应该这样做。