MS Access 2010 query using tempvar inside IN() condition - ms-access

Question

I am trying to filter a query using a temporary variable that is inside an IN() condition. The temporary variable contains a list of text values. I am using the macro-builder tool in Access 2010.
Assume I have a query qryMain that produces:
Field1 Field2
1 A
4 B
2 C
3 D
without a WHERE clause. Using the clause
WHERE [tblMain].[Field2] IN([TempVars]![tmpField2])
to filter the query, the desired results are
Field1 Field2
1 A
4 B
when tmpField2 is set to "A,B". I set tmpField2 using an on-click event in form frmMain using SetTempVar and Requery the subform/subreport object sfrmMain that is based on qryMain. This is done via the MS macro-builder, not VBA.
Unfortunately, requerying sfrmMain produces an empty table rather than the expected results. Note that if I set tmpField2 to "A", then the requery macro works as expected.
I have tried multiple variations of initializing tmpField2, based on Access's double quote requirements, but still no success. My question is similar to this as-yet unanswered question, but my question involves passing the temp variable inside an IN() statement within the WHERE clause, without using VBA.

Answer 1

The problem is not actually due to TempVars. If your value list came from a form's text box instead of TempVars, the result would be the same.
For what you're attempting to do, IN () requires a hard-coded list of values:
SELECT m.Field1, m.Field2
FROM tblMain AS m
WHERE m.Field2 IN ('A','B');
But, instead of a hard-coded list of values, you want to supply the list dynamically when the query is run:
WHERE m.Field2 IN (something_dynamic);
Unfortunately, Access will not cooperate. Whatever you supply for something_dynamic, Access will interpret it to be only one value ... not a list of values. And it doesn't matter what method you use to supply something_dynamic ... a TempVar, a text box, a formal query parameter, a custom VBA function which returns a string containing a list of values ... that list will be evaluated as only a single value.
If you were willing to use VBA, you could write the query at runtime to include a hard-coded value list before executing it. Since you want to avoid VBA, you can try something like this ...
WHERE InStr(1, [TempVars]![tmpField2], "'" & m.Field2 & "'") > 0
Note that approach requires quoting text values within tmpField2: 'A','B'
Also beware that approach could be painfully slow with a large table. Access would need to evaluate that InStr expression for every row in the table.