From: Nyasha Chigwamba <nyasha.chigwamba@voss-solutions.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
CC: "pgsql-performance@lists.postgresql.org"
	<pgsql-performance@lists.postgresql.org>
Subject: Re: LATERAL subquery predicate pushdown: filter applied after JSON
 construction instead of inside join (PG 18)
Thread-Topic: LATERAL subquery predicate pushdown: filter applied after JSON
 construction instead of inside join (PG 18)
Thread-Index: AQHcm2HpOCzn9hTYHUKXgqMXWD3NMrV9w3YAgAxxDIY=
Date: Mon, 23 Feb 2026 10:52:05 +0000
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Hi Tom,

Thank you for this - much appreciated. Removing the ORDER BY LIMIT does cha=
nge the query and after some further investigation, it looks like I also ne=
ed to project the raw columns then apply the filters on the projected colum=
ns as a opposed to filtering on the constructed JSONB.

Regards,
Nyasha
________________________________
From: Tom Lane <tgl@sss.pgh.pa.us>
Sent: February 11, 2026 12:37 PM
To: Nyasha Chigwamba <nyasha.chigwamba@voss-solutions.com>
Cc: pgsql-performance@lists.postgresql.org <pgsql-performance@lists.postgre=
sql.org>
Subject: Re: LATERAL subquery predicate pushdown: filter applied after JSON=
 construction instead of inside join (PG 18)

Nyasha Chigwamba <nyasha.chigwamba@voss-solutions.com> writes:
> Question: Can the planner push predicates on view columns into the underl=
ying LATERAL subqueries?

It can, but it will not push them into a subquery with LIMIT,
because that would potentially change the subquery result.

I'd try to get rid of all those ORDER BY LIMIT bits in your
view definition.  That's generally considered an antipattern
in SQL.  It's definitely an optimization fence.

                        regards, tom lane
This communication is confidential and if not addressed to you and has been=
 received in error, you must: (i) notify the sender immediately and delete =
the e-mail; and (ii) refrain from copying, printing, forwarding, publishing=
 or disclosing the contents of the e-mail.

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Hi Tom,</div>
<div style=3D"font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, =
Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" clas=
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<br>
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Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" clas=
s=3D"elementToProof">
Thank you for this - much appreciated. Removing the ORDER BY LIMIT does cha=
nge the query and after some further investigation, it looks like I also ne=
ed to project the raw columns then apply the filters on the projected colum=
ns as a opposed to filtering on
 the constructed JSONB.</div>
<div style=3D"font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, =
Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" clas=
s=3D"elementToProof">
<br>
</div>
<div style=3D"font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, =
Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" clas=
s=3D"elementToProof">
Regards,</div>
<div style=3D"font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, =
Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" clas=
s=3D"elementToProof">
Nyasha</div>
<div class=3D"elementToProof" id=3D"appendonsend"></div>
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11pt; color: rgb(0, 0, 0);" class=3D"elementToProof">
<b>From:</b>&nbsp;Tom Lane &lt;tgl@sss.pgh.pa.us&gt;<br>
<b>Sent:</b>&nbsp;February 11, 2026 12:37 PM<br>
<b>To:</b>&nbsp;Nyasha Chigwamba &lt;nyasha.chigwamba@voss-solutions.com&gt=
;<br>
<b>Cc:</b>&nbsp;pgsql-performance@lists.postgresql.org &lt;pgsql-performanc=
e@lists.postgresql.org&gt;<br>
<b>Subject:</b>&nbsp;Re: LATERAL subquery predicate pushdown: filter applie=
d after JSON construction instead of inside join (PG 18)</div>
<div style=3D"direction: ltr;" class=3D"elementToProof">&nbsp;</div>
</div>
<div style=3D"font-size: 11pt;" class=3D"elementToProof">Nyasha Chigwamba &=
lt;nyasha.chigwamba@voss-solutions.com&gt; writes:<br>
&gt; Question: Can the planner push predicates on view columns into the und=
erlying LATERAL subqueries?<br>
<br>
It can, but it will not push them into a subquery with LIMIT,<br>
because that would potentially change the subquery result.<br>
<br>
I'd try to get rid of all those ORDER BY LIMIT bits in your<br>
view definition.&nbsp; That's generally considered an antipattern<br>
in SQL.&nbsp; It's definitely an optimization fence.<br>
<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; regards, to=
m lane</div>
This communication is confidential and if not addressed to you and has been=
 received in error, you must: (i) notify the sender immediately and delete =
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