SQLSTATE 42P02Severity lowLab verified

Incident brief

Undefined parameter

A query referenced a positional parameter ($1, $2, ...) outside of any context that supplies a value for it. PostgreSQL had nothing to substitute.

What lands in your log

ERROR: there is no parameter $1

Reproduced on PostgreSQL 16.14Verified 2026-07-16 (Docker lab, PostgreSQL 16.14)Verified against PostgreSQL 16.14 in an isolated lab environment

In 10 seconds

What triggers it: Type a bare query containing $1 directly into a client, with no PREPARE/parameter binding around it.
Fix: Only use $1, $2, ... inside a PREPARE'd statement (then supply values via EXECUTE), or via your client library's real parameter-binding API.
Proof: Reproduced on PostgreSQL 16.14 → A bare SELECT $1 typed directly, with no surrounding PREPARE, was rejected with SQLSTATE 42P02. The session was unaffected afterward.

Fix

What to do right now

Application-level steps for this error.

Only use $1, $2, ... inside a PREPARE'd statement (then supply values via EXECUTE), or via your client library's real parameter-binding API.
Never paste a $n placeholder into ad-hoc SQL text and run it directly, there is nothing to bind it to.
A parameter-count mismatch caught later, at EXECUTE time, surfaces as a different SQLSTATE entirely, see the counterexample.

Fix SQL

PREPARE fetch_one(int) AS SELECT $1;
EXECUTE fetch_one(5);
DEALLOCATE fetch_one;

For this error

See this error live on the server

Run these against the affected instance to confirm the diagnosis before you act.

Undefined parameter (42P02) is statement-local: PostgreSQL does not retain the rejected value after the statement ends. Capture the exact bound value and statement position in application/server logs, then run this targeted validation before retrying.

Inspect prepared statement parameter slots

Validate the specific value/shape that can raise this SQLSTATE.

SELECT name, parameter_types, statement
FROM pg_prepared_statements
ORDER BY prepare_time;

Reproduce & verify

A real, single-session PostgreSQL reproduction

A literal transcript of SQL run against a live PostgreSQL instance in an isolated lab. The commands below are exactly what was executed.

1Type a bare query containing $1 directly into a client, with no PREPARE/parameter binding around it.
2PostgreSQL has no value bound to $1 in this context.
3SQLSTATE 42P02 is reported, naming the missing parameter.

One client: type $1 directly into a plain query, outside any PREPARE/parameter context.

Schema setup

-- No table needed: the failure happens purely at the parse stage.
SELECT 'no schema required' AS setup_note;

The unbound parameter reference

SELECT $1;

Confirming the session still works

SELECT 1 AS session_still_alive;

What PostgreSQL actually returned

Schema setup output

     setup_note     
--------------------
 no schema required
(1 row)

The unbound parameter reference output

ERROR:  there is no parameter $1
LINE 1: SELECT $1;
               ^

Confirming the session still works output

 session_still_alive 
----------------------
                    1
(1 row)

Verification

PG 16.14

Last verified: 2026-07-16 (Docker lab, PostgreSQL 16.14)
Verification scope: Verified against PostgreSQL 16.14 in an isolated lab environment
Audit status: reviewed

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Undefined parameter

What to do right now

See this error live on the server

Inspect prepared statement parameter slots

What PostgreSQL is telling you

A real, single-session PostgreSQL reproduction

A subtler mistake was tested directly: declaring fewer parameter types in PREPARE than the number of $n placeholders actually used in the query body.

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