How to check a value for paramter query

Question

I am passing a paramter value from my text box to my sql statement and I would like to check if the value is entered into a text box. If you have any idea please share it with me, i have been struggling with this for many days.Code below is how i try to check if the value is entered but I do not know how to check the value in the :VendorName
thanks
If Not txtVendorName.Text = "" Then
Sql = Sql & " AND (Upper(V.VNAMEL) LIKE '%' || Trim(Upper(:VendorName))|| '%') "
End If

Answer 1

Sorry guys english is not my first language and i will try to be clear and specific.
I have a search page where customeres can do searching either using a text box or two dropdowns i have on my page. they have the option of doing search either using a text box or dropdowns or both.Everything seems to work fine but if users does not leave the text box blank. but they leave the text box blank and do searching using the two dropdowns then the page comes up empty and i checked my query and i should get a value. Attacehed my code for you to look at it.
<pre>
Sub VendorSearch()
gvSearch.Visible = True
Dim MinPDate As String = drPur.SelectedItem.ToString
Dim MaxMDate As String = drPurM.SelectedItem.ToString
Dim liThisOne As ListItem
Dim strState As String = ""
For Each liThisOne In lstState.Items
If liThisOne.Selected Then
strState = strState & "'" & liThisOne.Value & "'" & ","
End If
Next
Dim Sql As String = " SELECT distinct V.VENDOR ""Vendor Id"",R.ADDRNUM,V.VNAMEL ""Vendor Name"",R.AADDR1,R.ACITY,R.VASST1, "
Sql = Sql & "R.ASTATE State,R.AZIPCODE, to_char(Max(P.DATEPUR),'YYYY/DD/MM') ""Plan Purchased Date"" , "
Sql = Sql & "TRIM (r.aaddr1 || decode(trim(r.aaddr2),null,'',' - ') || r.aaddr2) Address,"
Sql = Sql & " substr(decode(trim(r.vasst1),null, 'N/A','000/000-0000?','N/A','000/000-0000','N/A', r.vasst1),1,12) Fax, "
Sql = Sql & " substr(decode(trim(r.aphone),null, 'N/A','000/000-0000?','N/A', r.aphone),1,12)Phone "
Sql = Sql & "FROM VENDOR V,VENDADDR R, PLANHOLD P "
Sql = Sql & "WHERE V.VENDOR = R.VENDOR AND P.VENDOR = R.VENDOR "
Sql = Sql & " AND (P.DATEPUR >= TO_DATE('1999-01-01','YYYY-MM-DD')) "
Sql = Sql & "AND P.DATEPUR In ( select Max(P.DATEPUR) from PLANHOLD P where P.vendor = R.VENDOR) "
'If txtVendorName.Text <> "" Then
' Sql = Sql & " AND (Upper(V.VNAMEL) LIKE '%' || Trim(Upper(:VendorName))|| '%') "
'End If
If (strState.Length > 0 And lstState.SelectedIndex <> 0) Then
strState = Left(strState, strState.Length - 1)
strState = "(" & strState & ")"
Sql = Sql & "AND R.ASTATE IN " & strState
End If
If (drPur.SelectedIndex <> 0 And drPurM.SelectedIndex <> 0) Then
Sql = Sql & " AND to_number(to_char(p.datepur, 'YYYY')) between " & "'" & MinPDate & "'" & " AND " & "'" & MaxMDate & "'"
End If
' Dim Para As String
' SqlDataSource1.SelectParameters.
If Not txtVendorName.Text = "" Then
Sql = Sql & " AND (Upper(V.VNAMEL) LIKE '%' || Trim(Upper(:VendorName))|| '%') "
End If
'If Not IsDBNull(SqlDataSource1.SelectParameters(":VendorName")).val Then
' Sql = Sql & " AND (Upper(V.VNAMEL) LIKE '%' || Trim(Upper(:VendorName))|| '%') "
'End If
Sql = Sql & " AND V.VOBSOLET = 'N' "
Sql = Sql & "GROUP BY V.VENDOR, R.ADDRNUM,V.VNAMEL,R.AADDR1,R.AADDR2,R.ACITY,R.ASTATE, R.AZIPCODE, R.APHONE, R.VASST1, P.DATEPUR "
Sql = Sql & "ORDER BY V.VENDOR "
Response.Write("Sql " & "<br/>" & Sql & "<hr/>")
SqlDataSource1.SelectCommand = Sql
End Sub
</pre>