当我调用该函数时,我收到一条错误信息 data is null. This method or property cannot be called on null values.
我相信这一行存在错误
Error = id = rd.GetString(0);
我正在使用的代码如下
public string MaxId() { string id=""; con.Open(); string sql = "SELECT MAX(CustID) FROM Customer"; SqlCommand cmd = new SqlCommand(sql,con); SqlDataReader rd = cmd.ExecuteReader(); while(rd.Read()) { id = rd.GetString(0); } con.Close(); return id; }
如何从DataReader获取可能为null的字符串?