VB.NET 2005如何判断空值

[skidtren]

代码如下
Dim obj As Object = System.DBNull.Value
Dim sql As String = "select department1 from Information_System_department where dele_log='" + "S" + "' and company_id='" + s + " and department2='" + obj + "' "
sqlada = New SqlDataAdapter(sql, Me.sqlcon)
ds1 = New DataSet
ds1.Clear()
sqlada.Fill(ds1)

偶的department2的字段是空值.这样做查不出数据来.数据库中是有department2的字段是空值的(SQL中看到的是isnull)

高人指点一下什么改?
偶只有这么几分了

[hery2002]

  Dim sql As String = "select department1 from Information_System_department where dele_log='" + "S" + "' and company_id='" + s + " and ( department2 is null or  department2  ='') "

[vlsm]

Dim obj As string =""

[yuqingtong]

Dim sql As String = "select department1 from Information_System_department where dele_log='" + "S" + "' and company_id='" + s + " and ( isnull(department2,'') = '') "