I am trying to update field F1 in table T1 with the results from a
summation query Q1. Q1 is most definitely not updateable. The update is
simply a join from T1 to Q1 on the primary key with only F1 in the
actual update.

Access97 tells me the query must be updatable. Left-Joining T1 to Q1
does not help. I normally simply wrap this in a trx in code, but am
curious how to beat this seemingly simple operation.

SQL (noting that the query Q1 is non-updatable):

UPDATE T1
LEFT JOIN Q1
ON T1.PK = Q1.FK
SET
T1.F1 = IIf([Q1.F2=0,True,False);

thanks!