如何在c#中修改特定的单元格值mysql表？

Question

我有桌子

itemID	storeID	qty
103	LAB	20

我想添加特定项目的数量，例如：仓库'LAB'中存储的'103'。

 public void addQuantity(string store, string item, int qty) 
        {
            con.Open();

            string sql = "SELECT qty,warehouse.storeID,item.itemID FROM Item,warehouse,stocker WHERE stocker.storeID=warehouse.storeID AND stocker.itemID=item.itemID AND warehouse.storeID='"+store+"' AND Item.itemID='"+item+"' ";


            using (MySqlDataAdapter adapter = new MySqlDataAdapter(sql, con))
            {
                using (DataTable tempTable = new DataTable())
                {
                    adapter.Fill(tempTable);
                    if (tempTable.Rows.Count == 0) throw new Exception("No such product");
                    foreach (DataRow r in tempTable.Rows)
                    {
                        int newQty = (int)r["qty"] + qty;
                        if (newQty > 0)
                        {
                            r["qty"] = newQty;
                            qty = 0;
                            break;
                        }
                        else 
                        {
                            MessageBox.Show("error");
                        }

                    }
                    using (MySqlCommandBuilder cb = new MySqlCommandBuilder(adapter))
                    {
                        adapter.UpdateCommand = cb.GetUpdateCommand();// there is error
                        adapter.Update(tempTable);
                    }
                }
            }
            con.Close();
        
        }

它说：“多个基表不支持动态 SQL 生成”。

你有什么建议？

Answer 1

如果qty是整数列，你可以尝试：

将其当前值增加某个值：

using (var updateCommand = new MySqlCommand())
{
    updateCommand.CommandText = "UPDATE mytable t SET t.qty = t.qty + @newQty WHERE *...Your WHERE clause...*`"
    updateCommand.Parameters.AddWithValue("@newQty", newQtyValue);`
    // ...
}

或者追加全新的值：

using (var updateCommand = new MySqlCommand())
{
    updateCommand.CommandText = "UPDATE mytable t SET t.qty = @newQtyValue WHERE *...Your WHERE clause...*`"
    updateCommand.Parameters.AddWithValue("@newQtyValue", newQtyValue);`
    // ...
}

正如@sticky bit所说，最好使用Command.Parameters.AddWithValue而不是字符串连接/插值。