fix: MATCH ... CREATE ... RETURN creates once per row (GQLITE-T-0488)

src/backend/executor/query_dispatch.c

@@ -2874,7 +2874,6 @@ static int handle_match_create_return(cypher_executor *executor, cypher_query *q
 {
     if (unwind_before_create(query) || create_props_need_pipeline(query))
         return handle_rowwise_write(executor, query, result, flags);
-    (void)flags;
     cypher_match *match = find_match_clause(query);
     cypher_create *create = find_create_clause(query);
     cypher_return *ret = find_return_clause(query);
@@ -3014,11 +3013,13 @@ static int handle_match_create_return(cypher_executor *executor, cypher_query *q
         return 0;
     }
 
-    int rc = execute_match_create_return_query(executor, match, create, ret, result);
-    if (rc >= 0) {
-        result->success = true;
-    }
-    return rc;
+    /* The legacy path ran MATCH + CREATE, then the MATCH again for the
+     * RETURN: the RETURN saw the new nodes, and a CREATE that bound no
+     * matched variable ran once for every row, or for no row
+     * (GQLITE-T-0488). The row pipeline runs the CREATE once per row and
+     * returns those rows. */
+    (void)match;
+    return handle_rowwise_write(executor, query, result, flags);
 }
 
 static int handle_match_return(cypher_executor *executor, cypher_query *query,

tests/functional/106_create_per_row_return.sql

@@ -0,0 +1,39 @@
+-- ========================================================================
+-- Test 106: MATCH ... CREATE ... RETURN creates once per row
+--           (GQLITE-T-0488)
+-- ========================================================================
+-- PURPOSE: when the created pattern bound no variable that the RETURN read,
+--          the CREATE ran once, and the RETURN ran the MATCH again after
+--          the write (it saw the new node). A MATCH with no rows and an
+--          aggregate RETURN still created a node.
+-- NOTE:    Assertions are hard: _assert has CHECK (ok = 1), so under
+--          `sqlite3 -bail` any failed expectation aborts the run.
+-- ========================================================================
+
+.load ./build/graphqlite
+
+SELECT '=== Test 106: CREATE per row with RETURN ===' as test_section;
+
+CREATE TEMP TABLE _assert(name TEXT, ok INTEGER CHECK (ok = 1));
+
+SELECT cypher('CREATE (:S106 {id: 1}), (:S106 {id: 2})') as setup;
+
+INSERT INTO _assert SELECT 'RETURN gives the MATCH rows only',
+    json(cypher('MATCH (a:S106) CREATE (a)-[:T]->(:N106) RETURN a.id AS id ORDER BY id'))
+    = json('[{"id":1},{"id":2}]');
+INSERT INTO _assert SELECT 'one node per row',
+    json(cypher('MATCH (n:N106) RETURN count(n) AS c')) = json('[{"c":2}]');
+
+INSERT INTO _assert SELECT 'aggregate RETURN counts the rows',
+    json(cypher('MATCH (a:S106) CREATE (:M106 {k: a.id}) RETURN count(*) AS c'))
+    = json('[{"c":2}]');
+INSERT INTO _assert SELECT 'aggregate RETURN: one node per row',
+    json(cypher('MATCH (n:M106) RETURN count(n) AS c')) = json('[{"c":2}]');
+
+INSERT INTO _assert SELECT 'no rows: count is 0',
+    json(cypher('MATCH (a:Missing106) CREATE (:Z106) RETURN count(*) AS c'))
+    = json('[{"c":0}]');
+INSERT INTO _assert SELECT 'no rows: nothing created',
+    json(cypher('MATCH (n:Z106) RETURN count(n) AS c')) = json('[{"c":0}]');
+
+SELECT 'Test 106 passed: ' || count(*) || ' assertions' AS result FROM _assert;

tests/metamorphic/known.json

@@ -10,6 +10,5 @@
   {"relation": "^expr_context/(head|reduce|call)/", "kind": "mismatch", "task": "GQLITE-T-0482"},
   {"relation": "^expr_context/.*/nested", "kind": "mismatch", "task": "GQLITE-T-0483"},
   {"relation": "^expr_context/", "kind": "mismatch", "query": "reverse\\(", "task": "GQLITE-T-0483"},
-  {"relation": "^expr_context/", "kind": "mismatch", "query": "reduce\\(acc = ''", "task": "GQLITE-T-0481"},
-  {"relation": "^write_return/", "kind": "mismatch", "query": "CREATE (\\(\\w+\\)-\\[:\\w+[^\\]]*\\]->)?\\(:New", "task": "GQLITE-T-0488"}
+  {"relation": "^expr_context/", "kind": "mismatch", "query": "reduce\\(acc = ''", "task": "GQLITE-T-0481"}
 ]