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();
}
}
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Answer
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
{
}
}
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
sure that was for example.