C#如何连接Mysql数据库？详解报错异常和增删改查

string sql = "select count(*) from user";

MySqlCommand cmd = new MySqlCommand(sql, conn);

Object result=cmd.ExecuteScalar();//执行查询，并返回查询结果集中第一行的第一列。所有其他的列和行将被忽略。select语句无记录返回时，ExecuteScalar()返回NULL值if (result != null)

{    int count = int.Parse(result.ToString());

}

string sql = "insert into user(username,password,registerdate) values('啊宽','123','"+DateTime.Now+"')";//string sql = "delete from user where userid='9'";//string sql = "update user set username='啊哈',password='123' where userid='8'";MySqlCommand cmd = new MySqlCommand(sql,conn);int result =cmd.ExecuteNonQuery();//3.执行插入、删除、更改语句。执行成功返回受影响的数据的行数，返回1可做true判断。执行失败不返回任何数据，报错，下面代码都不执行

String connetStr = "server=127.0.0.1;user=root;password=root;database=minecraftdb;";

MySqlConnection conn = new MySqlConnection(connetStr);

conn.Open();//必须打开通道之后才能开始事务MySqlTransaction transaction = conn.BeginTransaction();//事务必须在try外面赋值不然catch里的transaction会报错:未赋值Console.WriteLine("已经建立连接");try{    string date = DateTime.Now.Year + "-" + DateTime.Now.Month + "-" + DateTime.Now.Day;    string sql1= "insert into user(username,password,registerdate) values('啊宽','123','" + date + "')";

    MySqlCommand cmd1 = new MySqlCommand(sql1,conn);

    cmd1.ExecuteNonQuery();    string sql2 = "insert into user(username,password,registerdate) values('啊宽','123','" + date + "')";

    MySqlCommand cmd2 = new MySqlCommand(sql2, conn);

    cmd2.ExecuteNonQuery();

}catch (MySqlException ex)

{

    Console.WriteLine(ex.Message);

    transaction.Rollback();//事务ExecuteNonQuery()执行失败报错，username被设置unique

    conn.Close();

}finally{    if (conn.State != ConnectionState.Closed)

    {

        transaction.Commit();//事务要么回滚要么提交，即Rollback()与Commit()只能执行一个

        conn.Close();

    }

}