一、不同字串定義方式
      1）直接定義字串並連線
      `static SqlConnection conn;//定義連線物件
      public static SqlConnection Connection//連線物件的屬性
    {
        get
        {
            if (conn == null)
            {
                string connstr = "Data Source = (local); uid=sa;pwd=12345678;Initial Catalog =data_db; Integrated Security=SSPI";//本地連線  
                conn = new SqlConnection(connstr);
                conn.Open();
            }
            else if (conn.State == ConnectionState.Closed)
            {
                conn.Open();
            }
            else if (conn.State == ConnectionState.Broken)
            {
                conn.Close();
                conn.Open();
            }
            return conn;
        }
    }`
 

2）字串儲存在app.config檔案中定義
app.config檔案中新增：



資料庫連線類中引用：
public static string connstr = ConfigurationManager.ConnectionStrings["ConStr"].ConnectionString; static SqlConnection conn; public static SqlConnection Connection//連線物件的屬性 { get { if (conn == null) { string connstr = ConfigurationManager.ConnectionStrings["ConStr"].ConnectionString; conn = new SqlConnection(connstr); conn.Open(); } else if (conn.State == ConnectionState.Closed) { conn.Open(); } else if (conn.State == ConnectionState.Broken) { conn.Close(); conn.Open(); } return conn; }

二、連線字串各種情況下的定義
1）SQL身份驗證方式的本地資料庫連線
string strSqlConnect = “Data Source = (local); uid=sa;pwd=12345678;Initial Catalog =data_db; Integrated Security=SSPI”;
2）Windows身份驗證方式的本地資料庫連線
string strSqlConnect = “Data Source = (local); Initial Catalog =data_db; Integrated Security=SSPI”;
3）SQL身份驗證方式的遠端資料庫連線
string strSqlConnect = string.Format(@“server={0};uid=sa;pwd=12345678;database=data_db;Trusted_Connection=no”, ip + “,1433”);//使用IP遠端登入
其中：ip為伺服器IP地址，要確保你所使用的埠號在遠端伺服器上已經開放。