From: bertrand HARTWIG <hartwig.bertrand@gmail.com>
Message-Id: <CD2A2F2D-30A2-450E-BA84-58A79860CEFF@gmail.com>
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Subject: Re: How to definitively determine whether a statement is a SELECT
 statement?
Date: Tue, 1 Sep 2026 07:07:17 +0200
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 <CANzqJaA9uF7JEyqmJ6JVuoadnAqU2=56VXC7stqJeTdpm6ozFQ@mail.gmail.com>
Cc: Pgsql-admin <pgsql-admin@lists.postgresql.org>
To: Ron Johnson <ronljohnsonjr@gmail.com>
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Hello,

You can use this python lib : pglast

from pglast import parse_sql
from pglast.ast import SelectStmt


def is_select_query(sql: str) -> bool:
    try:
        statements =3D parse_sql(sql)
    except Exception:
        return False  # SQL invalide

    if len(statements) !=3D 1:
        return False  # Refuse plusieurs instructions SQL

    return isinstance(statements[0].stmt, SelectStmt)


print(is_select_query("SELECT * FROM users"))          # True
print(is_select_query("WITH x AS (SELECT 1) SELECT * FROM x"))  # True
print(is_select_query("INSERT INTO users(name) VALUES ('Alice')"))  # =
False
print(is_select_query("SELECT 1; DELETE FROM users"))  # False

Bertrand

> Le 31 ao=C3=BBt 2026 =C3=A0 18:06, Ron Johnson =
<ronljohnsonjr@gmail.com> a =C3=A9crit :
>=20
> Sometimes, the developers add comments to the top of statements, and =
so we see that in pg_stat_activity.query as seen in this example:
>=20
> select query
> from pg_stat_activity
> where pid =3D 1054079;
>  query =20
> ----------------------------------------
> -- Some comment written by the developer
> SELECT blah blah FROM .blah
>=20
> I could case-insensitively search pg_stat_activity.query for "SELECT " =
but that will fail if there is a SELECT in the CTE or subquery of a =
DELETE or UPDATE statement, and writing a parser to strip out all =
comments is a bit too much effort for a simple query.
>=20
> --
> Death to <Redacted>, and butter sauce.
> Don't boil me, I'm still alive.
> <Redacted> lobster!


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<html aria-label=3D"message body"><head><meta http-equiv=3D"content-type" =
content=3D"text/html; charset=3Dutf-8"></head><body =
style=3D"overflow-wrap: break-word; -webkit-nbsp-mode: space; =
line-break: after-white-space;">Hello,<div><br></div><div>You can use =
this python lib :&nbsp;<span style=3D"color: rgb(78, 201, 176); =
font-family: Menlo, Monaco, &quot;Courier New&quot;, monospace; =
white-space: pre; background-color: rgb(18, 19, =
20);">pglast</span><div><br></div><div><div>from pglast import =
parse_sql</div><div>from pglast.ast import =
SelectStmt</div><div><br></div><div><br></div><div>def =
is_select_query(sql: str) -&gt; bool:</div><div>&nbsp; &nbsp; =
try:</div><div>&nbsp; &nbsp; &nbsp; &nbsp; statements =3D =
parse_sql(sql)</div><div>&nbsp; &nbsp; except =
Exception:</div><div>&nbsp; &nbsp; &nbsp; &nbsp; return False &nbsp;# =
SQL invalide</div><div><br></div><div>&nbsp; &nbsp; if len(statements) =
!=3D 1:</div><div>&nbsp; &nbsp; &nbsp; &nbsp; return False &nbsp;# =
Refuse plusieurs instructions SQL</div><div><br></div><div>&nbsp; &nbsp; =
return isinstance(statements[0].stmt, =
SelectStmt)</div><div><br></div><div><br></div><div>print(is_select_query(=
"SELECT * FROM users")) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;# =
True</div><div>print(is_select_query("WITH x AS (SELECT 1) SELECT * FROM =
x")) &nbsp;# True</div><div>print(is_select_query("INSERT INTO =
users(name) VALUES ('Alice')")) &nbsp;# =
False</div><div>print(is_select_query("SELECT 1; DELETE FROM users")) =
&nbsp;# =
False</div><div><br></div><div>Bertrand</div></div><div><br><blockquote =
type=3D"cite"><div>Le 31 ao=C3=BBt 2026 =C3=A0 18:06, Ron Johnson =
&lt;ronljohnsonjr@gmail.com&gt; a =C3=A9crit :</div><br =
class=3D"Apple-interchange-newline"><div><div dir=3D"ltr"><div>Sometimes, =
the developers add comments to the top of statements, and so we see that =
in&nbsp;<span =
style=3D"font-family:monospace">pg_stat_activity.</span><span =
style=3D"font-family:monospace">query</span><font face=3D"arial, =
sans-serif"> as seen in this =
example:</font></div><div><br></div><div><font face=3D"monospace">select =
query<br>from pg_stat_activity<br>where pid =3D 1054079;<br>&nbsp;query =
&nbsp;<br>----------------------------------------</font></div><div><font =
face=3D"monospace">-- Some comment written by the developer<br>SELECT =
blah blah FROM .blah</font></div><div><br></div><div>I could =
case-insensitively search&nbsp;pg_stat_activity.query for "SELECT " but =
that will fail if there is a SELECT in the CTE or subquery of a DELETE =
or UPDATE statement, and writing a parser to strip out all comments is a =
bit too much effort for a simple query.</div><div><br></div><span =
class=3D"gmail_signature_prefix">-- </span><br><div dir=3D"ltr" =
class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div =
dir=3D"ltr">Death to &lt;Redacted&gt;, and butter sauce.<div>Don't boil =
me, I'm still alive.<br><div><div>&lt;Redacted&gt; =
lobster!</div></div></div></div></div></div>
</div></blockquote></div><br></div></body></html>=

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