"Circular reference caused by ..." error in Access SQL (but not in T-SQL) - sql

Question

I have the following SQL statement which returns the desired result in SQL Server 2012:
SELECT
S.ONOMA
, S.DIEY
, S.POLH
, S.TK
, S.IDIOT
, S.KODIKOS
, S.AFM
FROM
SYNERG AS S
INNER JOIN
(SELECT
G.AFM, MIN(KODIKOS) AS KODIKOS
FROM SYNERG AS G
WHERE LEN(ISNULL(AFM, '')) != 0
GROUP BY AFM) AS I ON S.KODIKOS = I.KODIKOS
ORDER BY
S.AFM
but when I run the same SQL statement in MS Access 2007 I get an error:
Circular reference caused by 'KODIKOS' in query definition's SELECT list.
Any help would be appreciated.

Answer 1

As explained in the link by HansUp:
The alias of a calculated field cannot be identical to any of the field names used to calculate the field.
This can be rather annoying (esp. if it is a field that is returned by the query), but there is no way around it.
So you need to change the alias, e.g.:
SELECT
S.ONOMA
, S.DIEY
, S.POLH
, S.TK
, S.IDIOT
, S.KODIKOS
, S.AFM
FROM
SYNERG AS S
INNER JOIN
(SELECT
G.AFM, MIN(KODIKOS) AS MinKODIKOS
FROM SYNERG AS G
WHERE LEN(Nz(AFM, '')) <> 0
GROUP BY AFM) AS I ON S.KODIKOS = I.MinKODIKOS
ORDER BY
S.AFM
Note also that an IsNull() function exists in Access, but has a different meaning (it takes one argument and returns a Boolean). The corresponding function is Nz()
And (thanks #HansUp), the unequal operator is <>, not !=. I always use <> in SQL Server too, no need to make things more complicated than necessary. :)