SQL 选择多个总和？

Question

假设我有一张 table :

SELECT  SUM(quantity) AS items_sold_since_date,
        product_ID
FROM    Sales
WHERE order_date >= '01/01/09'
GROUP BY product_ID

这将返回自特定日期以来销售数量的产品列表。有没有办法不仅选择这个总和，而且还选择没有 where 条件的总和？我希望查看每种产品自特定日期以来的销售情况以及所有(不受日期限制)的销售情况。

Answer 1

SELECT  SUM(CASE WHEN order_date >= '01/01/09' THEN quantity ELSE 0 END) AS items_sold_since_date,
        SUM(quantity) AS items_sold_total,
        product_ID
FROM    Sales
GROUP BY product_ID