本文介绍了我收到错误“将数据类型 nvarchar 转换为实数时出错."的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我的代码如下，请告诉我问题出在哪里，以便我们可以按仓库 ID 降价 7%?
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
当你的 仓库 ID 和 折扣率 由最终用户指定，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
{
}
}
我还建议您重新考虑您的查询，因为它会使用相同的值更新所有产品价格，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
当然是这样.
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