How to use iif in query criteria

[ali_sh]

Hello
I want to add a criteria in a query under field_2 to return value larger than field_1
I wrote

>field_1

and that was ok but it is possible for field_1 to be null
so I wrote following code and got error

IIf(IsNull(field_1);field_2;>field_1))

Can anyone help me on this?
Thanks in advance

[June7]

Operator symbols cannot be dynamic.

>Nz(field_1;0)

[ali_sh]

Operator symbols cannot be dynamic.

>Nz(field_1;0)

Thank you very much It is a brilliant way but I have positive and negative value in any amount and I also want to use similar way in search form for null text box.
I have a search form containing a text box and I want to filter a field based on value greater than value entered in text box but return all the field when the text box is empty.
What do you do in this situation?
Is there any other way to do this? by using SQL or add a column or using "between" operators or ...?
I'll be very grateful if you help me on this

[June7]

I never use dynamic parameterized query. I use VBA to build filter criteria and apply to form or report. Review http://allenbrowne.com/ser-62.html