diff --git a/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlAstBuilder.java b/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlAstBuilder.java
index 4a88ab9c2..d555a0ad6 100644
--- a/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlAstBuilder.java
+++ b/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlAstBuilder.java
@@ -66,6 +66,22 @@ public abstract class SparqlAstBuilder {
      */
     private final Set<String> blankNodeLabels = new HashSet<>();
 
+    /** Unique IDs for basic graph patterns, including those in nested groups. */
+    private int bgpScopeCounter;
+
+    /**
+     * Current BGP scope at each group depth. FILTER preserves the enclosing scope,
+     * including when its expression contains EXISTS or NOT EXISTS. Other graph
+     * patterns, BIND, and inline VALUES end the preceding BGP.
+     */
+    private final Deque<Integer> bgpScopeIdStack = new ArrayDeque<>();
+
+    /**
+     * First BGP using each explicit label. Shared across subqueries and update
+     * WHERE clauses, but excludes CONSTRUCT and update templates.
+     */
+    private final Map<String, Integer> blankNodeLabelToBgpScope = new HashMap<>();
+
     /**
      * Stack of currently open SELECT operations (top-level SELECT and nested SELECT subqueries).
      */
@@ -345,6 +361,7 @@ public void enterWhereClause() {
      */
     public void enterGroup() {
         groupStack.push(new ArrayList<>());
+        bgpScopeIdStack.push(++bgpScopeCounter);
         if (selectWhereGroupFollows && hasCurrentSelect()) {
             selectWhereGroupDepths.push(groupStack.size());
             selectWhereGroupFollows = false;
@@ -369,11 +386,13 @@ && hasCurrentSelect()
                 && depthBeforePop == selectWhereGroupDepths.peek()) {
             selectWhereGroupDepths.pop();
             List<PatternAst> popped = groupStack.pop();
+            bgpScopeIdStack.pop();
             getCurrentSelectFrame().whereClause = new GroupGraphPatternAst(popped);
             return;
         }
 
         List<PatternAst> popped = groupStack.pop();
+        bgpScopeIdStack.pop();
         GroupGraphPatternAst group = new GroupGraphPatternAst(popped);
         appendClosedGroup(group);
     }
@@ -388,6 +407,8 @@ private void appendClosedGroup(GroupGraphPatternAst group) {
         } else if (!existsGroupDepths.isEmpty() && groupStack.size() == existsGroupDepths.peek()) {
             existsGroupDepths.pop();
             capturedExistsStack.push(group);
+            // An expression's graph pattern does not end the enclosing BGP.
+            return;
         } else if (!serviceStack.isEmpty() && groupStack.size() == serviceStack.peek().groupDepth()) {
             ServiceEntry entry = serviceStack.pop();
             currentGroup().add(new ServiceAst(entry.endpoint(), entry.silent(), group));
@@ -397,9 +418,19 @@ private void appendClosedGroup(GroupGraphPatternAst group) {
         } else if (groupStack.isEmpty()) {
             if (hasCurrentSelect()) getCurrentSelectFrame().whereClause = group;
             else whereClause = group;
+            return;
         } else {
             currentGroup().add(group);
         }
+        renewBgpScope();
+    }
+
+    /** Starts a fresh BGP after a non-FILTER graph pattern in the current group. */
+    private void renewBgpScope() {
+        if (!bgpScopeIdStack.isEmpty()) {
+            bgpScopeIdStack.pop();
+            bgpScopeIdStack.push(++bgpScopeCounter);
+        }
     }
 
     /**
@@ -458,6 +489,7 @@ public void addInlineValues(ValuesAst values) {
             throw new IllegalStateException("addInlineValues() called outside of a group graph pattern");
         }
         currentGroup().add(values);
+        renewBgpScope();
     }
 
     /**
@@ -483,6 +515,7 @@ public void addBind(BindAst bind) {
                     "Variable ?" + name + " used in BIND is already declared in the same group graph pattern");
         }
         group.add(bind);
+        renewBgpScope();
     }
 
     // --- Optional ---
@@ -656,6 +689,18 @@ public TermAst termFromBlankNode(SparqlParser.BlankNodeContext ctx) {
         }
         String label = ctx.getText();
         blankNodeLabels.add(label);
+        // Templates are built outside graph-pattern groups. Their labels are
+        // independent of WHERE labels; update-template restrictions are checked
+        // separately by UpdateTemplateValidator. CONSTRUCT WHERE opens a group
+        // explicitly, so its abbreviated WHERE still participates in this check.
+        if (!bgpScopeIdStack.isEmpty()) {
+            Integer currentScope = bgpScopeIdStack.peek();
+            Integer registeredScope = blankNodeLabelToBgpScope.putIfAbsent(label, currentScope);
+            if (registeredScope != null && !registeredScope.equals(currentScope)) {
+                throw new QuerySyntaxException(
+                        "Blank node label '" + label + "' is used in more than one basic graph pattern");
+            }
+        }
         return this.iri(label);
     }
 
diff --git a/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/listener/SelectQueryAstListener.java b/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/listener/SelectQueryAstListener.java
index ed4f3a7ed..f4476a619 100644
--- a/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/listener/SelectQueryAstListener.java
+++ b/src/main/java/fr/inria/corese/core/next/query/impl/sparql/parser/listener/SelectQueryAstListener.java
@@ -1,6 +1,8 @@
 package fr.inria.corese.core.next.query.impl.sparql.parser.listener;
 
+import fr.inria.corese.core.next.common.text.RdfText;
 import fr.inria.corese.core.next.generated.antlr.SparqlParser;
+import fr.inria.corese.core.next.query.api.exception.QuerySyntaxException;
 import fr.inria.corese.core.next.query.impl.sparql.parser.SparqlAstBuilder;
 import fr.inria.corese.core.next.query.impl.sparql.parser.SparqlQueryAstBuilder;
 import fr.inria.corese.core.next.query.impl.sparql.parser.semantic.support.VariableScopeAnalyzer;
@@ -8,6 +10,7 @@
 
 import java.util.ArrayList;
 import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -83,23 +86,29 @@ private void extractProjection(SparqlParser.SelectClauseContext ctx) {
             queryBuilder().setProjectionAll();
             return;
         }
-        List<String> allVars = new ArrayList<>();
+        Set<String> projectedVariables = new LinkedHashSet<>();
         List<String> expressionBoundVars = new ArrayList<>();
         Map<String, TermAst> expressionTerms = new LinkedHashMap<>();
         Map<String, Set<String>> expressionReferencedVariables = new LinkedHashMap<>();
         for (SparqlParser.SelectVarContext selectVar : ctx.selectVar()) {
             if (selectVar.expression() != null) {
                 // (expr AS ?var) — introduces a new variable, not projected from WHERE
-                String varName = selectVar.var_().getText();
-                allVars.add(varName);
+                String varName = RdfText.stripVariableMarker(selectVar.var_().getText());
+                if (!projectedVariables.add(varName)) {
+                    throw new QuerySyntaxException(
+                        "Variable ?" + varName + " introduced by SELECT expression is already projected");
+                }
                 expressionBoundVars.add(varName);
                 TermAst expressionAst = builder().termFromExpression(selectVar.expression());
                 expressionTerms.put(varName, expressionAst);
                 expressionReferencedVariables.put(varName, variableScopeAnalyzer.collectReferencedVariables(expressionAst));
             } else if (selectVar.var_() != null) {
-                allVars.add(selectVar.var_().getText());
+                String varName = RdfText.stripVariableMarker(selectVar.var_().getText());
+                // SPARQL 1.1 section 18.2.4.4 accumulates plain variables in a set.
+                // A later plain reference to an earlier alias is also permitted.
+                projectedVariables.add(varName);
             }
         }
-        queryBuilder().setProjectionVariables(allVars, expressionBoundVars, expressionTerms, expressionReferencedVariables);
+        queryBuilder().setProjectionVariables(new ArrayList<>(projectedVariables), expressionBoundVars, expressionTerms, expressionReferencedVariables);
     }
 }
diff --git a/src/test/java/fr/inria/corese/core/next/query/impl/sparql/execution/NextSparqlPipelineScopeExecutorTest.java b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/execution/NextSparqlPipelineScopeExecutorTest.java
new file mode 100644
index 000000000..02b88c1df
--- /dev/null
+++ b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/execution/NextSparqlPipelineScopeExecutorTest.java
@@ -0,0 +1,76 @@
+package fr.inria.corese.core.next.query.impl.sparql.execution;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+
+import fr.inria.corese.core.next.data.api.term.BNode;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+/** Result-level regressions for blank-node scopes and SELECT projection sets. */
+class NextSparqlPipelineScopeExecutorTest extends PipelineTestSupport {
+
+    @ParameterizedTest
+    @ValueSource(strings = { "?x ?x", "?x $x", "$x ?x" })
+    void repeatedProjectionProducesOneColumn(String projection) {
+        try (var result = executor.evaluateTuple("SELECT " + projection + " WHERE { VALUES ?x { 1 } }")) {
+            assertEquals(List.of("x"), result.getBindingNames());
+            assertTrue(result.hasNext());
+            assertEquals("1", result.next().getValue("x").stringValue());
+            assertFalse(result.hasNext());
+        }
+    }
+
+    @Test
+    void projectedAliasMayBeReferencedAgain() {
+        try (var result = executor.evaluateTuple("SELECT (1 AS ?x) $x (?x + 1 AS ?y) WHERE {}")) {
+            assertEquals(List.of("x", "y"), result.getBindingNames());
+            assertTrue(result.hasNext());
+            var row = result.next();
+            assertEquals("1", row.getValue("x").stringValue());
+            assertEquals("2", row.getValue("y").stringValue());
+            assertFalse(result.hasNext());
+        }
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "FILTER EXISTS { ?s <http://example.org/knows> ?o }",
+            "FILTER NOT EXISTS { ?s <urn:missing> ?o }"
+    })
+    void blankNodeStillJoinsTriplesAcrossExistsFilter(String filter) {
+        insert(iri(ALICE), iri(NAME), valueFactory.createLiteral("Alice"));
+        insert(iri(BOB), iri(NAME), valueFactory.createLiteral("Bob"));
+        try (var result = executor.evaluateTuple("""
+                SELECT ?name WHERE {
+                  _:a <http://example.org/knows> ?friend .
+                  %s
+                  _:a <http://example.org/name> ?name
+                }
+                """.formatted(filter))) {
+            assertTrue(result.hasNext());
+            assertEquals("Alice", result.next().getValue("name").stringValue());
+            assertFalse(result.hasNext(), "The same blank-node label must join on the same subject");
+        }
+    }
+
+    @Test
+    void constructLabelCreatesAFreshNodeInsteadOfReusingTheWhereBinding() {
+        try (var result = executor.evaluateGraph("""
+                CONSTRUCT { _:a <urn:friend> ?friend }
+                WHERE { _:a <http://example.org/knows> ?friend }
+                """)) {
+            assertTrue(result.hasNext());
+            var triple = result.next();
+            assertInstanceOf(BNode.class, triple.getSubject());
+            assertEquals(iri("urn:friend"), triple.getPredicate());
+            assertEquals(iri(BOB), triple.getObject());
+            assertFalse(result.hasNext());
+        }
+    }
+}
diff --git a/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserBlankNodeScopeTest.java b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserBlankNodeScopeTest.java
new file mode 100644
index 000000000..0ac8db50d
--- /dev/null
+++ b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserBlankNodeScopeTest.java
@@ -0,0 +1,101 @@
+package fr.inria.corese.core.next.query.impl.sparql.parser;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import fr.inria.corese.core.next.query.api.exception.QuerySyntaxException;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+/** SPARQL 1.1 sections 5.1.1, 16.2.1, 18.2.2, and 19.6. */
+class SparqlParserBlankNodeScopeTest {
+
+    private final SparqlParser parser = new SparqlParser();
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "",
+            "FILTER (?x != ?y)",
+            "FILTER EXISTS { ?s ?p ?o }",
+            "FILTER NOT EXISTS { ?s ?p ?o }",
+            "FILTER (EXISTS { ?s ?p ?o } && NOT EXISTS { ?t ?q ?r })",
+            "FILTER EXISTS { _:inner <urn:p> ?v . OPTIONAL { ?s ?p ?o } }",
+            "FILTER EXISTS { _:inner <urn:p> ?v . FILTER EXISTS { ?s ?p ?o } _:inner <urn:q> ?w }"
+    })
+    void filtersPreserveTheEnclosingBasicGraphPattern(String filter) {
+        String query = "SELECT * WHERE { _:a <urn:p> ?x . " + filter + " _:a <urn:q> ?y }";
+        assertDoesNotThrow(() -> parser.parse(query));
+        assertTrue(parser.validate(query).isValid());
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "{}",
+            "{ ?s ?p ?o }",
+            "OPTIONAL { ?s ?p ?o }",
+            "MINUS { ?s ?p ?o }",
+            "GRAPH <urn:g> { ?s ?p ?o }",
+            "SERVICE <urn:service> { ?s ?p ?o }",
+            "{ ?s ?p ?o } UNION { ?t ?q ?r }",
+            "{ SELECT ?s WHERE { ?s ?p ?o } }",
+            "BIND (1 AS ?z)",
+            "BIND (EXISTS { ?s ?p ?o } AS ?z)",
+            "VALUES ?z { 1 }"
+    })
+    void nonFilterPatternsEndThePrecedingBasicGraphPattern(String pattern) {
+        assertInvalidLabelReuse("SELECT * WHERE { _:a <urn:p> ?x . " + pattern + " _:a <urn:q> ?y }");
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "SELECT * WHERE { _:a <urn:p> ?x . OPTIONAL { _:a <urn:q> ?y } }",
+            "SELECT * WHERE { _:a <urn:p> ?x . FILTER EXISTS { _:a <urn:q> ?y } }",
+            "SELECT * WHERE { _:a <urn:p> ?x . FILTER NOT EXISTS { _:a <urn:q> ?y } }",
+            "SELECT * WHERE { FILTER EXISTS { _:a <urn:p> ?x } _:a <urn:q> ?y }",
+            "SELECT * WHERE { { _:a <urn:p> ?x } UNION { _:a <urn:q> ?y } }",
+            "SELECT * WHERE { { SELECT ?x WHERE { _:a <urn:p> ?x } } _:a <urn:q> ?y }",
+            "SELECT * WHERE { GRAPH <urn:g> { _:a <urn:p> ?x } GRAPH <urn:h> { _:a <urn:q> ?y } }",
+            "CONSTRUCT { _:a <urn:p> ?x } WHERE { _:a <urn:p> ?x . OPTIONAL { _:a <urn:q> ?y } }",
+            "INSERT {} WHERE { _:a <urn:p> ?x }; INSERT {} WHERE { _:a <urn:q> ?y }"
+    })
+    void labelsCannotBeSharedByDistinctBasicGraphPatterns(String query) {
+        assertInvalidLabelReuse(query);
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "CONSTRUCT { _:a <urn:p> ?x . _:a <urn:q> ?x } WHERE { _:a <urn:r> ?x }",
+            "CONSTRUCT WHERE { _:a <urn:p> ?x . _:a <urn:q> ?y }",
+            "INSERT { _:a <urn:p> ?x } WHERE { _:a <urn:q> ?x }",
+            "INSERT { _:a <urn:p> ?x } WHERE { ?s <urn:q> ?x }; INSERT { _:a <urn:q> ?x } WHERE { ?s <urn:p> ?x }",
+            "INSERT DATA { _:a <urn:p> 1 . GRAPH <urn:g> { _:a <urn:q> 2 } }",
+            "SELECT * WHERE { [] <urn:p> ?x . OPTIONAL { [] <urn:q> ?y } }",
+            "SELECT * WHERE { _:a <urn:p> ?x . OPTIONAL { _:b <urn:q> ?y } _:c <urn:r> ?z }"
+    })
+    void templatesAndAnonymousNodesHaveIndependentScopes(String query) {
+        assertDoesNotThrow(() -> parser.parse(query));
+    }
+
+    @Test
+    void insertDataStillRejectsLabelsReusedAcrossOperations() {
+        assertThrows(QuerySyntaxException.class, () -> parser.parse(
+                "INSERT DATA { _:a <urn:p> 1 }; INSERT DATA { _:a <urn:q> 2 }"));
+    }
+
+    @Test
+    void scopeStateDoesNotLeakBetweenParserInvocations() {
+        String query = "SELECT * WHERE { _:a <urn:p> ?x }";
+        assertDoesNotThrow(() -> parser.parse(query));
+        assertInvalidLabelReuse("SELECT * WHERE { _:a <urn:p> ?x . OPTIONAL { _:a <urn:q> ?y } }");
+        assertDoesNotThrow(() -> parser.parse(query));
+    }
+
+    private void assertInvalidLabelReuse(String query) {
+        QuerySyntaxException error = assertThrows(QuerySyntaxException.class, () -> parser.parse(query));
+        assertTrue(error.getMessage().contains("Blank node label '_:a'"), error.getMessage());
+        assertFalse(parser.validate(query).isValid());
+    }
+}
diff --git a/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserProjectionScopeTest.java b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserProjectionScopeTest.java
new file mode 100644
index 000000000..41932a1ee
--- /dev/null
+++ b/src/test/java/fr/inria/corese/core/next/query/impl/sparql/parser/SparqlParserProjectionScopeTest.java
@@ -0,0 +1,64 @@
+package fr.inria.corese.core.next.query.impl.sparql.parser;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+
+import fr.inria.corese.core.next.query.api.exception.QuerySyntaxException;
+import fr.inria.corese.core.next.query.impl.sparql.ast.SelectQueryAst;
+import fr.inria.corese.core.next.query.impl.sparql.ast.VarAst;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+/** SPARQL 1.1 sections 4.1.3 and 18.2.4.4: projection is a set, aliases must be new. */
+class SparqlParserProjectionScopeTest {
+
+    private final SparqlParser parser = new SparqlParser();
+
+    @ParameterizedTest
+    @ValueSource(strings = { "?x ?y ?x ?y", "?x $x ?y $y", "$x ?y ?x $y" })
+    void plainVariablesAreDeduplicatedInFirstOccurrenceOrder(String projection) {
+        SelectQueryAst ast = assertInstanceOf(SelectQueryAst.class,
+                parser.parse("SELECT " + projection + " WHERE { ?x <urn:p> ?y }"));
+        assertEquals(List.of(new VarAst("x"), new VarAst("y")), ast.projection().variables());
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = { "(1 AS ?x) ?x", "(1 AS $x) ?x $x", "(1 AS ?x) $x" })
+    void plainReferencesMayFollowAnAlias(String projection) {
+        SelectQueryAst ast = assertInstanceOf(SelectQueryAst.class,
+                parser.parse("SELECT " + projection + " WHERE {}"));
+        assertEquals(List.of(new VarAst("x")), ast.projection().variables());
+        assertTrue(ast.projection().expressionBoundVariables().contains("x"));
+        assertEquals(1, ast.projection().expressionTerms().size());
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "?x (1 AS ?x)", "?x (1 AS $x)", "$x (1 AS ?x)",
+            "(1 AS ?x) (2 AS ?x)", "(1 AS ?x) (2 AS $x)", "(1 AS $x) (2 AS ?x)"
+    })
+    void aliasesCannotRedefineAnEarlierProjectedVariable(String projection) {
+        String query = "SELECT " + projection + " WHERE {}";
+        assertThrows(QuerySyntaxException.class, () -> parser.parse(query));
+        assertFalse(parser.validate(query).isValid());
+        assertThrows(QuerySyntaxException.class, () -> parser.parse("SELECT * WHERE { { " + query + " } }"));
+    }
+
+    @Test
+    void projectionScopesAreIndependentAcrossSubqueries() {
+        String query = "SELECT ?x $x WHERE { { SELECT ?x $x WHERE { ?x ?p ?o } } }";
+        SelectQueryAst ast = assertInstanceOf(SelectQueryAst.class, parser.parse(query));
+        assertEquals(List.of(new VarAst("x")), ast.projection().variables());
+    }
+
+    @Test
+    void aliasesStillCannotRedefineVariablesFromWhere() {
+        assertFalse(parser.validate("SELECT (1 AS $x) WHERE { ?x ?p ?o }").isValid());
+    }
+}