MySqlConnection: 连接MySQL服务器数据库。 MySqlCommand:执行一条sql语句。 MySqlDataReader: 包含sql语句执行的结果，并提供一个方法从结果中阅读一行。 MySqlTransaction: 代表一个SQL事务在一个MySQL数据库。 MySqlException: MySQL报错时返回的Exception。 MySqlCommandBuilder: Automatically generates single-table commands used to reconcile changes made to a DataSet with the associated MySQL database. MySqlDataAdapter: Represents a set of data commands and a database connection that are used to fill a data set and update a MySQL database. MySqlHelper: Helper class that makes it easier to work with the provider 

using MySql.Data.MySqlClient;  String connetStr = "server=127.0.0.1;port=3306;user=root;password=root; database=minecraftdb;"; // server=127.0.0.1/localhost 代表本机，端口号port默认是3306可以不写 MySqlConnection conn = new MySqlConnection(connetStr); try {           conn.Open();//打开通道，建立连接，可能出现异常,使用try catch语句       Console.WriteLine("已经建立连接");       //在这里使用代码对数据库进行增删查改 } catch (MySqlException ex) {       Console.WriteLine(ex.Message); } finally {       conn.Close(); } 

连接错误时MySqlConnection会返回一个MySqlException，其中包括2个变量: 　　Message: A message that describes the current exception. 　　Number: The MySQL error number. (0: Cannot connect to server. 1045: Invalid user name and/or password.)             catch (MySqlException ex) {     switch (ex.Number)     {         case 0:         Console.WriteLine("Cannot connect to server.  Contact administrator");         break;     case 1045:         Console.WriteLine("Invalid username/password, please try again");         break;     } } 

string sql= "select * from user"; MySqlCommand cmd = new MySqlCommand(sql,conn); MySqlDataReader reader =cmd.ExecuteReader();//执行ExecuteReader()返回一个MySqlDataReader对象 while (reader.Read())//初始索引是-1，执行读取下一行数据，返回值是bool {     //Console.WriteLine(reader[0].ToString() + reader[1].ToString() + reader[2].ToString());     //Console.WriteLine(reader.GetInt32(0)+reader.GetString(1)+reader.GetString(2));     Console.WriteLine(reader.GetInt32("userid") + reader.GetString("username") + reader.GetString("password"));//"userid"是数据库对应的列名，推荐这种方式 } 

//string sql = "select * from user where username='"+username+"' and password='"+password+"'"; //我们自己按照查询条件去组拼 string sql = "select * from user where username=@para1 and password=@para2";//在sql语句中定义parameter，然后再给parameter赋值 MySqlCommand cmd = new MySqlCommand(sql, conn); cmd.Parameters.AddWithValue("para1", username); cmd.Parameters.AddWithValue("para2", password);  MySqlDataReader reader = cmd.ExecuteReader(); if (reader.Read())//如果用户名和密码正确则能查询到一条语句，即读取下一行返回true {     return true; } 　c.需要查询返回一个值        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 5.事务(MySqlTransaction类) 

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();     } }