c# - 将 Sum 列与另一列相乘

Question

我想要一个 SQL 代码从数据库中获取 Product_name,Sum(quantity),price 并将其显示到 winform 上的 datagridview。到目前为止，我有以下代码来获取数据:

conn.Open();
SqlDataAdapter da = new SqlDataAdapter("SELECT Prod_name, SUM(quantity) AS quantity, Price FROM Fatur GROUP BY Prod_name, Price ", conn);

DataSet ds = new DataSet();
da.Fill(ds);

dataGridView1.DataSource = ds.Tables[0];
conn.Close();

问题1是:如何在SQL代码中添加另一列乘法 Sum(quantity) * Price AS Total ？

我尝试了另一种方法，用上面的代码填充dataGridView1，并在dataGridView1中创建另一列，将数量列与价格相乘。这是代码

foreach(DataGridViewRow row in dataGridView1.Rows)
{
    row.Cells[0].Value = Convert.ToString(Convert.ToInt32(row.Cells[2].Value) * Convert.ToInt32(row.Cells[3].Value));
}

但它显示一个空列。

Answer 1

最好用 SQL 来做:

SELECT Prod_name,
  SUM(quantity) AS quantity,
  Price,
  SUM(quantity) * Price total
FROM Fatur
GROUP BY Prod_name,
  Price;

或者:

SELECT prod_name,
  quantity,
  price,
  quantity * price total
FROM
  (SELECT Prod_name,
    SUM(quantity) AS quantity,
    Price
  FROM Fatur
  GROUP BY Prod_name,
    Price
  );