MIME-Version: 1.0
From: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Date: Sat, 25 Apr 2026 10:11:40 -0700
Message-ID: 
 <CAHg+QDfUwNPcxWk_WJWPvVhrGAeeDQrD6CMTuFcSd1ybELie9Q@mail.gmail.com>
Subject: [PATCH] Improve error message for graph variable references in
 subqueries within GRAPH_TABLE
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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Hi Hackers,

When a subquery inside GRAPH_TABLE COLUMNS or MATCH WHERE references a
graph pattern variable, the error was a confusing "missing FROM-clause
entry for table".  Fix by walking the parentParseState chain in
transformGraphTablePropertyRef() to detect the graph variable and report
a clear "cannot be used in a subquery" error instead.


Based on the below comment and code in  transformRangeGraphTable I am
assuming we don't support
subqueries for now.

  /*
* If we support subqueries within GRAPH_TABLE, those need to be
* propagated to the queries resulting from rewriting graph table RTE. We
* don't do that right now, hence prohibit it for now.
*/
if (pstate->p_hasSubLinks)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("subqueries within GRAPH_TABLE reference are not supported")));
pstate->p_hasSubLinks = saved_hasSublinks;

Attached a patch to address this which also includes a test.

Thanks,
Satya

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<div dir=3D"ltr">Hi Hackers,<div><br></div><div>When a subquery inside GRAP=
H_TABLE COLUMNS or MATCH WHERE references a<br>graph pattern variable, the =
error was a confusing &quot;missing FROM-clause<br>entry for table&quot;.=
=C2=A0 Fix by walking the parentParseState chain in<br>transformGraphTableP=
ropertyRef() to detect the graph variable and report<br>a clear &quot;canno=
t be used in a subquery&quot; error instead.<br></div><div><br></div><div><=
br></div><div>Based on the below comment and code in=C2=A0

transformRangeGraphTable I am assuming we don&#39;t support</div><div>subqu=
eries for now.</div><div><br></div><div>=C2=A0=C2=A0/*</div>	 * If we suppo=
rt subqueries within GRAPH_TABLE, those need to be<br>	 * propagated to the=
 queries resulting from rewriting graph table RTE. We<br>	 * don&#39;t do t=
hat right now, hence prohibit it for now.<br>	 */<br>	if (pstate-&gt;p_hasS=
ubLinks)<br>		ereport(ERROR,<br>				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED)=
,<br>				 errmsg(&quot;subqueries within GRAPH_TABLE reference are not supp=
orted&quot;)));<br>	pstate-&gt;p_hasSubLinks =3D saved_hasSublinks;<br><br>=
Attached a patch to address this which also includes a test.<br><br>Thanks,=
<div>Satya<br><br><br></div></div>

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	name="0001-Improve-error-for-graph-variable-references-in-subqu.patch"
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