主题：关于Select的问题(已解决)

Dim S As String = e.Form.Controls("TextBox1").Value

Dim cmd As New SQLCommand

Dim dt As datatable

cmd.C  '外部数据源名称

cmd.CommandText = "SELECT * From {送货地址} Where [客户] = '"& S &"'" 

dt = cmd.ExecuteReader()

If dt.DataRows.Count > 0 Then

Messagebox.show("已经存在数据!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

Else

Messagebox.show("可以增加数据, !","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

End If

这段代码是判断外部数据中有无数据同文本框一样的,如果有就提示有(也就是账号存在的意思),如果没有就提示没有.

Dim cmd As New SQLCommand

Dim dt As datatable

cmd.C  

cmd.CommandText = "SELECT * From {xtuser} Where [用户账号] = '"& username &"'" 

dt = cmd.ExecuteReader()

If dt.DataRows.Count > 0 Then

Messagebox.show("账号已存在!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

Else

Messagebox.show("账号不存在, !","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

End If

cmd.C

这段代码的意思是只要符合账号和密码就可以登录,否则就是提示密码和账号不对.

Dim UserName As String = e.Form.Controls("账号1").Value

Dim Usermima As String = e.Form.Controls("密码1").Value

If UserName = ""  Then

    Messagebox.show("请输入用户名!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

    Return

ElseIf Usermima = ""  Then

    Messagebox.show("请输入登陆密码!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

    Return

ElseIf Usermima.Length <> 6 Then

    Messagebox.show("密码长度不足6位数!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

    Return

End If

Dim rdo1 As WinForm.RadioButton

Dim rdo2 As WinForm.RadioButton

rdo1 = e.Form.Controls("收银台")

rdo2 = e.Form.Controls("管理台")

Dim cmd As New SQLCommand

Dim dt As DataTable

Dim dr As DataRow

Dim dr1 As DataRow

cmd.C

cmd.CommandText = "Select * From {xtuser} Where [用户账号] = '" & UserName & "'And [用户密码] ='" & Usermima & "' And [登陆状态] = True "

dt = cmd.ExecuteReader()

If dt.DataRows.Count > 0 Then

    MessageBox.Show("该账号已经在另外登录登陆!", "温馨提示!")

    e.Form.Close()

Else

    Messagebox.show("该帐号在此终端登录!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

End If