15728 2012-01-26 08:59:22 +0000 [XQ30] Scope of variables defined in group-by 2013-06-19 09:13:05 +0000 1 1 1 Unclassified XPath / XQuery / XSLT XQuery 3.0 Member-only Editors Drafts PC All CLOSED FIXED P2 normal --- 1 mike jonathan.robie jim.melton jmdyck public-qt-comments oldest_to_newest 63149 0 mike 2012-01-26 08:59:22 +0000 The scope of variables declared in a group-by clause is governed by the general rules in 3.10.1: The scope of a bound variable includes all subexpressions of the containing FLWOR that appear after the variable binding. (This differs from the window clause, which has rules of its own). This means that it is legal to write: for $e in //employee group by $s := $e/salary, $t := string($s) But we don't say what this is supposed to mean. We say in 3.10.7: For each pre-grouping tuple, the grouping keys are computed by evaluating the expression in the GroupingSpec and atomizing the result. But $s is not present in the pre-grouping tuple, and therefore $t cannot be computed for a pre-grouping tuple. And we can't use the value of $s from the post-grouping tuple because that's only available after doing the grouping, and we can't do the grouping until we know $t. We could try to define some kind of model where the grouping is done in a sequence of steps each of which generates intermediate tuples, but it would be complex and probably lead to more surprises. Or we could try to do a syntactic transformation of the above to for $e in //employee let $s := $e/salary let $t := string($s) group by $s := $s, $t := $t (which is the reverse of the current transformation) As I can't see any practical uses that require this kind of construct, I think the simplest solution is to modify the scope rules so that in a group by clause, the variables declared within the clause are not in scope within that clause. We already have custom scope rules for the window clause, it's not a big deal to also introduce custom rules for the group by clause. 63169 1 jmdyck 2012-01-27 00:01:01 +0000 (For some previous discussion of this problem, see Bug 15044 comment #3 et seq.) 64726 2 jonathan.robie 2012-02-29 14:54:13 +0000 In yesterday's telcon, we agreed that: 1. This sentence does not apply to Group By: <quote>The scope of a bound variable includes all subexpressions of the containing FLWOR that appear after the variable binding.</quote> Grouping variables, like Windowing variables, have their own rules. 2. All bindings in group by expressions are computed before the group by clause is evaluated and are based on pre-grouping tuples. 3. Variables bound in one grouping spec in a group by clause can be used in other grouping specs, but these variables are also based on pre-grouping values. 4. Pre-grouping values are not implicitly atomized, post-grouping values are implicitly atomized.