The NZ function converts a Null to Zero; if an actual zero result is
displaying as blank, you should use the Format property of the Control and
make certain it does not have an entry for 0 that shows blank.
Larry Linson
Microsoft Access MVP
I could assume from your question that you have a Control on the Report with
a ControlSource of =Sum([SomeField]). It would be helpful if you'd include a
bit more detail with your question (but not enough to bury us in detail
<GRIN>).
If the values in [SomeField] are Null, then nothing will show. You could try
using as ControlSource the expression =
IIF(IsNull(Sum([SomeField]),"0",Sum([SomeField])) -- in a simple test case
where there were no "matching order detail records", thus giving a Null
summation, it worked for me.
Be sure to rename Controls so they do not have identical names to the
underlying Fields, if either are used in calculations.