如果更新值，则检查 Mysql 中的值

Question

我有一个数据库，其中包含一些名为 UPC 标题描述和数量的列。我正在尝试检查列中是否已经存在 UPC 编号，如果确实存在，则将该条目的数量更新为 1，这是我到目前为止所拥有的：

    MySqlConnection connection = new MySqlConnection(MyConString);
                connection.Open();
                MySqlCommand command = connection.CreateCommand();
                command.CommandText = "INSERT INTO tableName " +
                           "(upc, title, description, quantity) " +
                       "VALUES " +
                           "(@upc, @title, @description, @quantity)";
                MySqlCommand upcCheck = connection.CreateCommand();
                upcCheck.CommandText = "Select COUNT (*) FROM tableName WHERE " +
                    "(upc=@upc) LIMIT 1";
                upcCheck.Parameters.AddWithValue("@upc", upc.Text); //Checks for duplicate UPCs
                MySqlDataReader check = upcCheck.ExecuteReader();
                    if( check.Read() != false)
                    {
                        command.Parameters.AddWithValue("@quantity",++); //not sure how to word it right
                    }


                command.Parameters.AddWithValue("@upc", upc.Text); //adding parameters SAFELY to the statement
                command.Parameters.AddWithValue("@title", titlename);
                command.Parameters.AddWithValue("@description", descname);
                command.Parameters.AddWithValue("@quantity", "1");

                MySqlDataReader result = command.ExecuteReader();

我只是不知道如何用它来进行检查。

更新！这是工作代码。

    MySqlConnection connection = new MySqlConnection(MyConString);

                connection.Open();
                MySqlCommand updatecommand = connection.CreateCommand();

                updatecommand.CommandText = "UPDATE tableName Set quantity = quantity +1 " +
                    "WHERE upc = @upc";
                updatecommand.Parameters.AddWithValue("@upc", upc.Text);
                using (MySqlDataReader updateResult = updatecommand.ExecuteReader())
                {


                    if (updateResult.RecordsAffected == 0)
                    {
                        affected = true;
                    }
                    else
                    {
                        affected = false;
                    }
                }
                 if(affected == true)
                {

                    MySqlCommand command = connection.CreateCommand();
                    command.CommandText = "INSERT INTO tableName " +
                        "(upc, title, description, quantity) " +
                    "VALUES " +
                        "(@upc, @title, @description, @quantity)";
                    command.Parameters.AddWithValue("@upc", upc.Text);
                    command.Parameters.AddWithValue("@title", titlename);//adding parameters SAFELY to the statement
                    command.Parameters.AddWithValue("@description", descname);
                    command.Parameters.AddWithValue("@quantity", "1");



                    MySqlDataReader result = command.ExecuteReader();
                }

Answer 1

虽然我没有专门使用 MySqlDataReader，但我会稍微改变一下周围的查询……否则你为插入所使用的格式（参数化）完全没问题。

虽然 Hristo 提供的 ON DUPLICATE KEY UPDATE 很酷，但您可能会丢失其他列元素以供记录。我会改成..

MySqlCommand command = connection.CreateCommand();
command.CommandText = "UPDATE tableName Set Quantity = Quantity +1 " +
                           "WHERE upc = @upc"
command.Parameters.AddWithValue("@upc", upc.Text);

** 不知道 MySqlDataReader 将如何返回值/状态，但是

result = command.ExecuteReader();

if( the status indicates it actually succeeded in an update, 
    or how many records were updated > 0 )
  return;  // you've just increased the counter...

否则，它不在文件中。继续执行其余的 SQL 插入命令，我们可以覆盖最后一个命令实例...

command = connection.CreateCommand();
command.CommandText = "INSERT INTO tableName " +
                           "(upc, title, description, quantity) " +
                       "VALUES " +
                           "(@upc, @title, @description, @quantity)";

command.Parameters.AddWithValue("@upc", upc.Text);
command.Parameters.AddWithValue("@title", titlename);
command.Parameters.AddWithValue("@description", descname);
command.Parameters.AddWithValue("@quantity", "1");

result = command.ExecuteReader();

Answer 2

如果 UPC 是您的主键，您可以使用 MySQL 数据库的INSERT ON DUPLICATE KEY UPDATE 功能。如果您不想INSERT 新的UPC 只需运行UPDATE 查询，如果没有这样的行不会影响表中的数据。

UPDATE <tablename> SET quantity=quantity+1 WHERE UPC='<upc>'