ADQL/XML non compliance with SQL?

[Martin Hill]

I'm pretty sure this is correct (standard) SQL:

SELECT * FROM table t WHERE t.i=t.z AND t.i=t.a AND t.b=t.e

I would expect that an SQL database will look at those ANDs and work out which 
is the quickest set to solve first depending on internal indexing.

However ADQL/XML (and SADQL v1.0!) only allow pairwise ANDs.  When transforming 
  ADQL/XML -> Database SQL, we must use brackets around each boolean construct, 
because we don't know what the original priority might have been, ie:

    WHERE (f OR f) AND (t OR t) = f

is different from

    WHERE f OR (f AND t) OR t = t

and as soon as we use brackets we lose multiple Unions/Intersections.

We could work with the backend ADQL/XML->Database SQL transformations to fix 
this, but I think it might be better if the schema represented the SQL 
'properly'.  Particularly as currently I expect it's the ADQL/SQL -> ADQL/XML 
parser that is prioritising the brackets, rather than the backend.

So can I propose that IntersectionSearch and UnionSearch take 2..unbounded 
arguments?

On another point, isn't XOR a standard SQL boolean operator?

Cheers,

Martin

-- 
Martin Hill
Software Engineer
AstroGrid @ ROE
Tel: +44 7901 55 24 66
www.astrogrid.org