Re: [PATCH] rewriteGraphTable: Fix missing RTEs in FROM clause by setting inFromCl=true

On Thu, Mar 19, 2026 at 9:17 PM zengman <zengman(at)halodbtech(dot)com> wrote:
>
> Hi all,
>
> I made a super simple extension `https://github.com/Z-Xiao-M/pg_pgq2sql` to get the equivalent SQL of PGQ queries – it simply calls `pg_get_querydef` after `QueryRewrite` to fetch the SQL text.
>
> However, I noticed that some FROM clauses were missing in the generated SQL statements.
>
> ```
> postgres=# SELECT * FROM pg_pgq2sql($$
> SELECT common_name
> FROM GRAPH_TABLE (
> social_graph
> MATCH (a IS users)-[]->(x IS users)<-[]-(b IS users)
> WHERE a.name = 'Alice' AND b.name = 'Bob'
> COLUMNS (x.name AS common_name)
> )
> $$);
> pg_pgq2sql
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> SELECT common_name +
> FROM LATERAL ( SELECT users_1.name AS common_name +
> WHERE users.id = follows.follower AND users_1.id = follows.following AND users_2.id = follows_1.follower AND users_1.id = follows_1.following AND users.name::text = 'Alice'::text AND users_2.name::text = 'Bob'::text) "graph_table"
> (1 row)
> ```
>
> I did a quick check and found the issue: some `rte->inFromCl` were set to `false` (should be `true` here). Here’s a quick patch to fix it:
>
> ```
> postgres(at)zxm-VMware-Virtual-Platform:~/code/postgres$ git diff
> diff --git a/src/backend/rewrite/rewriteGraphTable.c b/src/backend/rewrite/rewriteGraphTable.c
> index 06f2f3442d8..d43704ef233 100644
> --- a/src/backend/rewrite/rewriteGraphTable.c
> +++ b/src/backend/rewrite/rewriteGraphTable.c
> @@ -498,7 +498,7 @@ generate_query_for_graph_path(RangeTblEntry *rte, List *graph_path)
> */
> rel = table_open(pe->reloid, AccessShareLock);
> pni = addRangeTableEntryForRelation(make_parsestate(NULL), rel, AccessShareLock,
> - NULL, true, false);
> + NULL, true, true);
> table_close(rel, NoLock);
> path_query->rtable = lappend(path_query->rtable, pni->p_rte);
> path_query->rteperminfos = lappend(path_query->rteperminfos, pni->p_perminfo);
> ```
>
> After applying the patch, the FROM clause is now complete:
>
> ```
> postgres=# SELECT * FROM pg_pgq2sql($$
> SELECT common_name
> FROM GRAPH_TABLE (
> social_graph
> MATCH (a IS users)-[]->(x IS users)<-[]-(b IS users)
> WHERE a.name = 'Alice' AND b.name = 'Bob'
> COLUMNS (x.name AS common_name)
> )
> $$);
> pg_pgq2sql
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> SELECT common_name +
> FROM LATERAL ( SELECT users_1.name AS common_name +
> FROM users, +
> follows, +
> users users_1, +
> follows follows_1, +
> users users_2 +
> WHERE users.id = follows.follower AND users_1.id = follows.following AND users_2.id = follows_1.follower AND users_1.id = follows_1.following AND users.name::text = 'Alice'::text AND users_2.name::text = 'Bob'::text) "graph_table"
> (1 row)
>
> postgres=#
> postgres=# SELECT common_name
> FROM GRAPH_TABLE (
> social_graph
> MATCH (a IS users)-[]->(x IS users)<-[]-(b IS users)
> WHERE a.name = 'Alice' AND b.name = 'Bob'
> COLUMNS (x.name AS common_name)
> ) ;
> common_name
> -------------
> Charlie
> (1 row)
>
> postgres=# SELECT common_name
> FROM LATERAL ( SELECT users_1.name AS common_name
> FROM users,
> follows,
> users users_1,
> follows follows_1,
> users users_2
> WHERE users.id = follows.follower AND users_1.id = follows.following AND users_2.id = follows_1.follower AND users_1.id = follows_1.following AND users.name::text = 'Alice'::text AND users_2.name::text = 'Bob'::text) "graph_table";
> common_name
> -------------
> Charlie
> (1 row)
> ```
>
> Curious to hear your thoughts/suggestions on this.

I checked the comment:

* inFromCl marks those range variables that are listed in the FROM clause.
* It's false for RTEs that are added to a query behind the scenes, such
* as the NEW and OLD variables for a rule, or the subqueries of a UNION.

Even the RTEs are not directly listed in FROM, but as we are rewriting the
match pattern using join and where clause, I tend to agree with the fix.

>
> --
> regards,
> Man Zeng

--
Regards
Junwang Zhao