SQL 语法中是否有一种直接的方法可以在没有子查询的情况下在单个查询中编写它?是否有任何机会以这种方式获得性能?
SELECT ProductCount, COUNT(*) as Occurence
FROM (
SELECT OrderID, COUNT(DISTINCT ProductID) as ProductCount
FROM OrderLine
GROUP BY OrderID
) X
GROUP BY ProductCount
ORDER BY ProductCount