From 0c8b3fe278d6e821e441fb451f5452af77a4dae3 Mon Sep 17 00:00:00 2001
From: waterWang <672684719@qq.com>
Date: Sun, 23 Aug 2026 20:09:03 +0800
Subject: [PATCH] Fix entity-projection alias in WITH clause causing MATCH to
 fail

When a vertex variable is renamed via an entity-projection alias in a WITH
clause (e.g. WITH n AS alias0), a subsequent MATCH (alias0) failed with
"variable 'alias0' already exists". The alias was created as a target-list
entry but no transform_entity was registered for the alias name, so
find_variable could not find it.

Fix: in transform_cypher_node, when te != NULL && entity == NULL but the
variable is visible as a column from a previous clause (colNameToVar
returns non-NULL), return the column reference directly instead of
erroring. The caller creates the transform_entity, allowing subsequent
clauses to reference the aliased variable.

Fixes #2538
---
 regress/expected/cypher_match.out  | 20 +++++++++++++-------
 src/backend/parser/cypher_clause.c | 11 +++++++++++
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/regress/expected/cypher_match.out b/regress/expected/cypher_match.out
index ab51486b3..47c0c8089 100644
--- a/regress/expected/cypher_match.out
+++ b/regress/expected/cypher_match.out
@@ -2270,9 +2270,11 @@ ERROR:  variable "p" already exists
 LINE 1: ...cypher('cypher_match', $$ CREATE (p) WITH p MATCH p=() RETUR...
                                                              ^
 SELECT * FROM cypher('cypher_match', $$ CREATE p=() WITH p MATCH (p) RETURN p $$)as (p agtype);
-ERROR:  variable 'p' already exists
-LINE 1: ...pher('cypher_match', $$ CREATE p=() WITH p MATCH (p) RETURN ...
-                                                             ^
+                                   p                                    
+------------------------------------------------------------------------
+ [{"id": 281474976710669, "label": "", "properties": {}}::vertex]::path
+(1 row)
+
 SELECT * FROM cypher('cypher_match', $$ CREATE ()-[p:knows]->() WITH p MATCH p=() RETURN p $$)as (p agtype);
 ERROR:  variable "p" already exists
 LINE 1: ...r_match', $$ CREATE ()-[p:knows]->() WITH p MATCH p=() RETUR...
@@ -2297,7 +2299,8 @@ SELECT * FROM cypher('cypher_match', $$ MATCH (_) RETURN _ $$) as (a agtype);
  {"id": 281474976710659, "label": "", "properties": {"age": 3, "name": "orphan"}}::vertex
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
  {"id": 281474976710668, "label": "", "properties": {"name": "John"}}::vertex
-(10 rows)
+ {"id": 281474976710669, "label": "", "properties": {}}::vertex
+(11 rows)
 
 SELECT * FROM cypher('cypher_match', $$ MATCH () MATCH (_{name: "Dave"}) RETURN 0 $$) as (a agtype);
  a 
@@ -2312,7 +2315,8 @@ SELECT * FROM cypher('cypher_match', $$ MATCH () MATCH (_{name: "Dave"}) RETURN
  0
  0
  0
-(10 rows)
+ 0
+(11 rows)
 
 SELECT * FROM cypher('cypher_match', $$ MATCH () MATCH (_{name: "Dave"}) RETURN _ $$) as (a agtype);
                                       a                                       
@@ -2327,7 +2331,8 @@ SELECT * FROM cypher('cypher_match', $$ MATCH () MATCH (_{name: "Dave"}) RETURN
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
-(10 rows)
+ {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
+(11 rows)
 
 SELECT * FROM cypher('cypher_match', $$ MATCH (my_age_default_{name: "Dave"}) RETURN my_age_default_$$) as (a agtype);
                                       a                                       
@@ -2348,7 +2353,8 @@ SELECT * FROM cypher('cypher_match', $$ MATCH () MATCH (my_age_default_{name: "D
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
  {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
-(10 rows)
+ {"id": 281474976710667, "label": "", "properties": {"name": "Dave"}}::vertex
+(11 rows)
 
 -- these should fail as they are prefixed with _age_default_ which is only for internal use
 SELECT * FROM cypher('cypher_match', $$ MATCH (_age_default_) RETURN _age_default_ $$) as (a agtype);
diff --git a/src/backend/parser/cypher_clause.c b/src/backend/parser/cypher_clause.c
index 147e3e74e..c555d2989 100644
--- a/src/backend/parser/cypher_clause.c
+++ b/src/backend/parser/cypher_clause.c
@@ -6962,6 +6962,17 @@ static Expr *transform_cypher_node(cypher_parsestate *cpstate,
          */
         else if (te && !entity)
         {
+            /*
+             * If the variable is visible as a column from a previous clause
+             * (e.g. WITH n AS alias0 → MATCH (alias0)), it is an alias
+             * projection of an existing entity.  Return the column reference
+             * directly instead of erroring — the caller will create the
+             * transform_entity for it.
+             */
+            if (previous_clause_var != NULL)
+            {
+                return (Expr *)previous_clause_var;
+            }
             ereport(ERROR,
                     (errcode(ERRCODE_DUPLICATE_ALIAS),
                      errmsg("variable '%s' already exists", node->name),