DataSource Controls :: Update Field In Db?

I am facing problem in my update statement,

Dim abc As String
abc = Request.QueryString("str")
Dim userName As String = CStr(Session("user"))
Label2.Text = userName
Dim MyConnection As New OdbcConnection(ConnStr)
MyConnection.Open()
Dim MyCommand As New OdbcCommand
MyCommand.Connection = MyConnection
If MyCommand.CommandText = "Select userid from week where userid ='" & userName & "'" Then
MyCommand.CommandText = "Update week Set value = '" & abc & "' where userid ='" & userName & "'"
Else
MyCommand.CommandText = "INSERT INTO week (value, userid) VALUES('" & abc & "','" & userName & "')"
End If
MyCommand.ExecuteNonQuery()
MyConnection.Close()