Multiple Parameters used in a form to populate a query - a mystery

[Alf]

I am trying to create a query which makes a firm searchable by the the sector
it trades in, and its post code or county. e.g. Metal fabricators in Essex.
Using a parameter query, the design looks like this.

I would like to be able use an combination of these 3 criteria to find the
correct answers,

[Forms]![Search Form]![Sector] Or Like [Forms]![Search Form]![Sector] Is Null

---This one gets info from a combo box.

[Forms]![Search Form]![County] Or Like [Forms]![Search Form]![County] Is Null

---So does this one.

[Forms]![Search Form]![PostCode] & "*" Or Like [Forms]![Search
Form]![PostCode] Is Null

---This one from a text box, i want it to be able to be partially completed
i.e, typing in CO would bring up CO18, CO12, CO13 etc

For example Metal fabricators in Essex. Using a parameter query, the
design looks like this.

 

[Van T. Dinh]

I think the croteria should be:

[Forms]![Search Form]![Sector] Or [Forms]![Search Form]![Sector] Is Null

[Forms]![Search Form]![County] Or [Forms]![Search Form]![County] Is Null

Like [Forms]![Search Form]![PostCode] & "*"
Or [Forms]![Search Form]![PostCode] Is Null

(type as one line in the appropriate Columns of your Query Design grid.)

Note that the [Search Form] must be open when the Query is executed.