从数据库中删除并减去特定单元格中的数据

Question

I am creating a form page where I need to show data in data grid view. When the user adds any item from the grid view it should be minused from inventory and update inventory when user press add button.

The code that I am using is giving me this exception:

Additional information: Incorrect syntax near '='.

My code:

    private void btnMoveItem_Click(object sender, EventArgs e)
    {
        SqlConnection con2 = new SqlConnection(@"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=Northwind;Integrated Security=True");
        con2.Open();

        String Query1= "DELETE FROM Inventory WHERE id = " + tbID.Text + "";

        SqlCommand sqlcmd1 = new SqlCommand(Query1, con2);
        sqlcmd1.ExecuteNonQuery();

        SqlCommand sqlcmd = new SqlCommand("UPDATE Inventory SET Quantity = @Quantity" +"WHERE id= " + tbID, con2);
        sqlcmd.Parameters.AddWithValue("@Item", this.nudQuantity.Text);
        sqlcmd.ExecuteNonQuery();

        con2.Close();
    }

Answer 1

The error is that you concatenate two strings without space between.

But there are many other errors.

All user values should be a sql parameter with correct type. nudQuantity.Text must be parsed/validated. Maybe id too.

string connectionString = @"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=Northwind;Integrated Security=True";

using (var con2 = new SqlConnection(connectionString))
{
    con2.Open();
    var Query1 = "DELETE FROM Inventory WHERE id = @id";

    var sqlcmd1 = new SqlCommand(Query1, con2);
    sqlcmd1.Parameters.AddWithValue("@id", tbID.Text);
    sqlcmd1.ExecuteNonQuery();

    var sqlcmd = new SqlCommand("UPDATE Inventory SET Quantity = @Quantity WHERE id=@id", con2);
    sqlcmd.Parameters.AddWithValue("@id", tbID.Text);
    sqlcmd.Parameters.AddWithValue("@Quantity", int.Parse(nudQuantity.Text));

    sqlcmd.ExecuteNonQuery();       
}

You could also merge these two query in a single one.

This query should be more like what you need.

UPDATE Inventory SET Quantity = Quantity-@Quantity WHERE id=@id;
DELETE FROM Inventory WHERE id = @id AND Quantity <= 0;

But there are no check on product availability here. If @Quantity is greater than Quantity, then no error will be thrown.