afs commented on code in PR #2925:
URL: https://github.com/apache/jena/pull/2925#discussion_r1930805943


##########
jena-arq/src/main/java/org/apache/jena/sparql/engine/iterator/QueryIterLateral.java:
##########
@@ -292,17 +295,33 @@ public Op transform(OpTable opTable) {
             // By the assignment restriction, the binding only needs to be 
added to each row of the table.
             Table table = opTable.getTable();
             // Table vars.
-            List<Var> vars = new ArrayList<>(table.getVars());
-            binding.vars().forEachRemaining(vars::add);
-            TableN table2 = new TableN(vars);
+            List<Var> tableVars = table.getVars();
+            List<Var> vars = new ArrayList<>(tableVars);
+
+            // Track variables that appear both in the table and the binding.
+            List<Var> commonVars = new ArrayList<>();
+
+            // Index variables in a set if there are more than a few of them.
+            Collection<Var> tableVarsIndex = tableVars.size() > 4 ? new 
HashSet<>(tableVars) : tableVars;
+            binding.vars().forEachRemaining(v -> {
+                if (tableVarsIndex.contains(v)) {
+                    commonVars.add(v);
+                } else {
+                    vars.add(v);
+                }
+            });
+
+            List<Binding> bindings = new ArrayList<>(table.size());
             BindingBuilder builder = BindingFactory.builder();
             table.iterator(null).forEachRemaining(row->{
-                builder.reset();
-                builder.addAll(row);
-                builder.addAll(binding);
-                table2.addBinding(builder.build());
+                if (Algebra.compatible(row, binding, commonVars.iterator())) {

Review Comment:
   > For the sake of closing the issue, should I modify/simplify the logic
   
   Yes, please.
   
   > Well, the tradeoff to what extend existing implementations need to drive 
restrictions of new features in a standard.
   
   SHACL WG has started and SHACL Values Insertion (which is similar but 
different) will need SPARQL syntax level solution, which implies static rules 
for scoping. As will parameterized query.
   
   I hope, in spirit, these different situations have a related approach.



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