[back-sql] Problem with NOT search requests (ITS#2652)

[emmanuel.duru@atosorigin.com]

Full_Name: Emmanuel Duru
Version: 2.2.0 alpha
OS: solaris 8
URL: 
Submission from: (NULL) (195.68.44.148)


A search request like (!<some attribute>=<some value>) should select
the entries which do not have <some attribute>; with back-sql only
entries which have at least one value for <some attribute> are selected.
The problem is that the request to select candidate entries perform a
join on the attribute in the filter (excluding entries without the
attribute). Consequently, the search request (!<some attribute>=*) does
not select any entry.
[Pierangelo Masarati] This is a known limitation caused by the design of the
backend;
some filters may not generate complete queries.  We might need
to think about a different design, if feasible.