因为ExecuteScalar，如果没得到数据，值是DBNull.Value，而不是null 所以你要用：if (cmd.ExecuteScalar() != DBNull.Value)没有区别，得出的结果是一样的
object val = cmd.ExecuteScalar() 这一句造成的报错, val = null 因为我执行的是insert语句,而这个方法的功能是:只返回数据集的第一行第一列 解决方案: ①最简单的一种 在service层调用db.Execute这个方法而不是ExecuteScalar方法 ②在sql中增加一句sql代码,select 1; 即可。因为ExecuteScalar是返回数据集的第...
就是判断你这条语句:select * from userinfo where name = '" + textBox1.Text.Trim() + "'如果没有数据.即:cmd.ExecuteScalar()==null.则注册.如果有数据.就说明用户已存在..一般不写成null==cmd.ExecuteScalar()而写成:cmd.ExecuteScalar()==null
问cmd.executescalar()可以工作，但抛出ORA-25191异常EN2.解析 关键字try 以及except是 使用Python 解...
问cmd.executescalar()可以工作，但抛出ORA-25191异常EN2.解析 关键字try 以及except是 使用Python ...
{ connection.Open();} cmd = new SqlCommand(sql, connection);cmd.CommandTimeout = 600;if (null!=cmd.ExecuteScalar()){ //隐藏登录窗口 this.Visible=false;//创建并打开主界面 Main main=new Main();main.Tag=this.FindForm();SqlDataReader dr;cmd.CommandText=sql;dr=cmd.ExecuteReader(...
int SetMasterVolumeLevelScalar(float fLevel, System.Guid pguidEventContext); int j(); int GetMasterVolumeLevelScalar(out float pfLevel); int k(); int l(); int m(); int n(); int SetMute([MarshalAs(UnmanagedType.Bool)] bool bMute, System.Guid pguidEventContext); ...
string str=(string)cmd.ExecuteScalar(); 如果只有一个string类数据可以这样，效率很高 如果有很多数据，就要这样： DataTable dt = new DataTable(); SqlDataAdapter adp = new SqlDataAdapter(cmd); adp.Fill(dt); 把数据都取到数据表中
execute sp_executesql into Table-Valued function Execute Sql query based on condition using Case statement Execute SQL Query dynamically in multiple databases Executed as user:. The step was cancelled (stopped) as the result of a stop job request. ExecuteScalar returns 0 (null) but INSERT is ...
lib(new_scalar.obj) VC++ can't find source file even when dependency & include files point directly to it VC++ fatal error LNK1104: cannot open file ... xxx.lib. VC++ vcredist_x86.exe parameters VC++: how to detect windows OS is 32bit or 64 bit? VC90.MFC Not Found & Search ...