Question

是否可以在一个选择查询中生成总和？

这样的事情：

SELECT id, SUM(current_price - bought_price)*amount AS profit FROM purchase WHERE purchase_id = 1 GROUP BY id

我希望所有返回profit

的总和

Answer 1

这就是你要问的：

SELECT tmp.id, SUM(tmp.profit)
FROM (
  SELECT id, SUM(current_price - bought_price)*amount AS profit 
  FROM purchase 
  WHERE purchase_id = 1
  GROUP BY id 
) AS tmp

但结果与

相同

SELECT SUM(current_price - bought_price)*amount AS profit 
FROM purchase 
WHERE purchase_id = 1

Answer 2

这是您的查询：

SELECT id, SUM(current_price - bought_price)*amount AS profit
FROM purchase
WHERE purchase_id = 1
GROUP BY id ;

如果您想获得总利润，只需删除group by并重新定义sum()：

SELECT SUM(current_price*amount - bought_price*amount) AS profit
FROM purchase
WHERE purchase_id = 1;

编辑：

您也可以将其写为：

SELECT SUM((current_price - bought_price)*amount) AS profit
FROM purchase
WHERE purchase_id = 1;

顺便说一下，原始配方并不正确。您想要使用与group by相同的表单：

SELECT id, SUM((current_price - bought_price)*amount) AS profit
FROM purchase
WHERE purchase_id = 1
GROUP BY id;

您的版本存在的问题是amount取自id的任意行。如果每个purchase id只有一行，那么没问题。但是如果id有多行，那么问题中的查询将产生不确定的结果。（您正在使用记录为here的group by的MySQL扩展。）

Answer 3

SELECT id, SUM(current_price - bought_price)*amount 
AS profit FROM purchase WHERE purchase_id = 1 GROUP BY id WITH ROLLUP;

您可以对GROUP BY（http://dev.mysql.com/doc/refman/5.0/en/group-by-modifiers.html）使用WITH ROLLUP修饰符。因此，您将获得所有产品组的所有产品摘要和总计。

SUM的Mysql SUM

3 个答案: