Why does this access query work and the other does not? - sql

Question

I have a query that filters based on a boolean value on a form (Task Archived). The boolean value is stored as a long in the underlying table (only 0 and -1 are allowed).
I wanted to write a query that would either show only those records that are false (records not archived) or all records.
I would have expected the follwing query to work, but it does not... it returns only those records for which the archive field is set to True (-1):
SELECT tbl_Tasks.TaskID, tbl_Tasks.TArchive
FROM tbl_Tasks
WHERE (((tbl_Tasks.TArchive)=
IIf([Forms]![frm_Activity]![txtArchivedTaskDisplay]=0,False,
(tbl_Tasks.TArchive)=0 Or (tbl_Tasks.TArchive)=-1)));
The query below, which I would expect to show only those records that are True, in fact returns all records:
SELECT tbl_Tasks.TaskID, tbl_Tasks.TArchive
FROM tbl_Tasks
WHERE (((tbl_Tasks.TArchive)=
IIf([Forms]![frm_Activity]![txtArchivedTaskDisplay]=0,False,
(tbl_Tasks.TArchive)<>0)));
Why is this? What logic is access follwing here?

Answer 1

You cannot put SQL where condition within IIF. Anything within IIF will be evaluated if possible. Since you only have 0 or -1 below evaluation will always be true.
((tbl_Tasks.TArchive)=0 Or (tbl_Tasks.TArchive)=-1) => true
that's why you are only seeing TArchive = true
You could try something like this for your first query:
WHERE
tbl_Tasks.TArchive **<** IIf(displayArchivedOnly,0,1);
for the second one:
WHERE
tbl_Tasks.TArchive = [Forms]![frm_Activity]![txtArchivedTaskDisplay]
assuming your txtArchivedTaskDisplay holds either true or false value like a toggle button. but again, read more about how iif works.