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using用法和SqlCommand認識

using三種用法

private void button1_Click(object sender, EventArgs e)
{
    SqlConnection conn = null;
    //實現了IDisposable介面的物件,可以使用using進行資源管理(如:SqlDataAdapter、SqlDataReader、DataSet、SqlCommand)
    //using會在作用於結束的時候自動呼叫物件的dispose方法
    //1.
    using (SqlConnection conn = new SqlConnection("server=.;database=Login;uid=sa;pwd=coder"
)) { SqlCommand cmd = new SqlCommand(); cmd.CommandText = "sql 語句"; cmd.Connection = conn; conn.Open(); cmd.ExecuteScalar(); //conn.Close();//關閉的是程式和資料庫之間的連線, //conn.Dispose();//這個方法內部是呼叫了close方法的 } //2. using (conn = new SqlConnection("連線字串"
)) { } //3. conn = new SqlConnection("連線字串"); using (conn) { } }

SqlCommand認識

 //兩種方式功能一樣
 SqlCommand cmd=new SqlCommand(); cmd.Connetion=conn; cmd.CommandText=""; 
 SqlCommand cmd = new SqlCommand("",conn);
//兩種方式功能一樣
SqlCommand cmd=new SqlCommand();cmd.Connection=conn;
SqlCommand cmd = conn.CreateCommand();