Problem while taking column values from Excel using vb.net

[shivapadma]

i am having one problem when i am retrieving data from Excel using vb.net

following is the code

Imports Microsoft.Office.Core
Imports System.Runtime.InteropServices
Imports System.Data.OleDb
Public Class Form1
    Dim cmd1 As OleDbCommand
    Dim dr1 As OleDbDataReader
    Dim str As String=" "
    Try
            cn = New 
           OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data        
           Source=C:\Folder\example_excel.xls;Extended Properties=Excel 8.0;")
            'provider to be used when working with excel database
            cn.Open()

            cmd1 = New OleDbCommand("select * from emp where 
            rollno!="+str+"", cn)
            MsgBox("1")
            dr1 = cmd1.ExecuteReader()

        Catch
        End Try

when i am executing above code,i am getting error like
Syntax error (missing operator) in query expression 'rollno!='

i want to retrieve records with empty fields...
please help me in this problem...

[Telinstryata]

try 'rollNo <> '

!= is C# syntax for "not equals"

<> is SQL Query syntax for "not equal"

Also, put your code in code tags like the following, so it's easier to understand.

Imports Microsoft.Office.Core
Imports System.Runtime.InteropServices
Imports System.Data.OleDb
Public Class Form1
Dim cmd1 As OleDbCommand
Dim dr1 As OleDbDataReader
Dim str As String=" "
Try
cn = New
OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Data
Source=C:\Folder\example_excel.xls;Extended Properties=Excel 8.0;")
'provider to be used when working with excel database
cn.Open()

cmd1 = New OleDbCommand("select * from emp where
rollno!="+str+"", cn)
MsgBox("1")
dr1 = cmd1.ExecuteReader()

Catch
End Try

[Plater]

!= is still SQL syntax.
The problem looks to be that you are missing the first single quote ' after rollno!=