我收到错误“将数据类型 nvarchar 转换为实数时出错". [英] I get an error "Error converting data type nvarchar to real."
问题描述
我的代码在下面,你能告诉我问题出在哪里,以便我们可以通过仓库 ID 降价 7% 吗?
The code which I have is below, can you please inform me where the issue might be so we can drop the price by warehouse ID with 7%?
private void button4_Click(object sender, EventArgs e)
{
try
{
myConnection = new SqlConnection(frm.cs);
myCommand = new SqlCommand("update Inventory set Price=@Price where WarehouseCode=6", myConnection);
myConnection.Open();
myCommand.Parameters.AddWithValue("@Price", "@Price * 0.7");
myCommand.ExecuteNonQuery();
myConnection.Close();
MessageBox.Show("Update successfully!");
DisplayData();
if (myConnection.State == ConnectionState.Open)
{
myConnection.Dispose();
}
}
推荐答案
因为您没有在 C# 代码 中为 @Price
分配任何值,而您的 仓库 ID
和 Discount rate
由最终用户分配,我建议您的代码如下:
As you are not assigning any value to @Price
in the C# code while your Warehouse Id
and the Discount rate
are subject to be assigned by the end-user, I recommend your code be like this:
private void button4_Click(object sender, EventArgs e)
{
try
{
var discountRate = 0.07; //could be Convert.ToDouble(textBox1.Text) or something else
var warehouseId = 6; //again, could be Convert.ToInt32(textBox2.Text) or something else
myConnection = new SqlConnection(frm.cs);
myCommand = new SqlCommand("update Inventory set Price=Price*(1-@DiscountRate) " +
"where WarehouseCode=@WarehouseId", myConnection);
myConnection.Open();
myCommand.Parameters.AddWithValue("@DiscountRate", discountRate);
myCommand.Parameters.AddWithValue("@WarehouseId", warehouseId);
myCommand.ExecuteNonQuery();
myConnection.Close();
MessageBox.Show("Update successfully!");
DisplayData();
if (myConnection.State == ConnectionState.Open)
{
myConnection.Dispose();
}
}
catch
{
}
}
我还建议您再次考虑您的查询,因为它会用相同的值更新所有产品的价格,您可以考虑传递参数 @ProductId
并且您的查询是
I would also recommend you think again about your query as it will update all products price with the same value, you may consider passing parameter @ProductId
and your query be
update Inventory set Price=Price*(1-@DiscountRate)
where WarehouseCode=@WarehouseId and ProductCode=@ProductId
当然是例如.
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