[PATCH] rewriteGraphTable: Fix missing RTEs in FROM clause by setting inFromCl=true - Mailing list pgsql-hackers

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
simplycalls `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
quickpatch to fix it:
 

```
postgres@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. 

--
regards,
Man Zeng