Here's something I put together and in your case the default value of * is the key and don't allow the field to be blank (and use Like in your query).
The free downloadable sample database at www.bullschmidt.com/access uses the query by form concept so that on the invoices dialog one can optionally choose a rep, a customer, and perhaps a date range, click on a button that says "Input," and then have the invoice form open up showing all the invoices that match the criteria.
And here is how the query by form concept can work.
On the invoices dialog there are the following controls:
InvDateMin with DefaultValue of =DateSerial(Year(Date())-1,1,1)
InvDateMax with DefaultValue of =Date()
InvRepNum with DefaultValue of *
InvCustNum with DefaultValue of *
Also on the invoices dialog there is a command button called cmdInput to open the invoices form with the following code behind the OnClick property:
And of course there could be a button to open a report the same way:
DoCmd.OpenReport "rptInv", acViewPreview
The invoices form (frmInv) has RecordSource property of qryInv.
And the qryInv query's criteria for the InvDate field has:
Between [Forms]![frmInvDialog]![InvDateMin] And [Forms]![frmInvDialog]![InvDateMax]
And the qryInv query's criteria for the RepNum field has:
And the qryInv query's criteria for the CustNum field has:
One related point is that you probably wouldn't want to allow blanks (i.e. Nulls) in fields that are going to be used with Like in any criteria for that field. Otherwise the blanks wouldn't be shown.
For example (based on what is entered into a last name search field):
Like 'Smith' would show Smith records
Like '' would show no records (probably not what one would want)
Like '*' would show all records
And to counter that I like to have the search fields have a DefaultValue of * and not allow the search fields to be blank.
Or a more complicated solution would be to create the query's SQL statement dynamically so that the criteria on a particular field isn't used unless needed.
' Set strSQL.
strSQL = "SELECT * FROM MyTable WHERE (1=1)"
If Not IsNull(Rep) Then
strSQL = strSQL & " AND (Rep='" & Rep & "')"
If Not IsNull(Customer) Then
strSQL = strSQL & " AND (Customer='" & Customer & "')"