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.
In 10 seconds
- What
- Undefined parameter
- What triggers it
- Type a bare query containing $1 directly into a client, with no PREPARE/parameter binding around it.
- The 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.
The fix
What to do right now
The immediate, application-level response to 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.
PREPARE fetch_one(int) AS SELECT $1;
EXECUTE fetch_one(5);
DEALLOCATE fetch_one;Diagnose
See it live on the server
Run these against the affected instance to confirm the diagnosis before you act.
Standard triage — not specific to this error
These are canonical PostgreSQL system-catalog queries, shown as SQL to run. No sample output is attached because this is general triage, not a captured lab transcript.This SQLSTATE does not have an error-specific live snapshot yet. These are the canonical system-catalog queries you run against the affected server to see the problem in real time — standard triage, not a reproduced transcript.
What is running right now
Active backends, how long each has been running, and what it is waiting on.
SELECT pid,
state,
wait_event_type,
wait_event,
now() - query_start AS running_for,
left(query, 80) AS query
FROM pg_stat_activity
WHERE state <> 'idle'
AND pid <> pg_backend_pid()
ORDER BY running_for DESC NULLS LAST;Who is blocking whom
Turn raw blocking PIDs into the actual queries on both sides of the wait.
SELECT blocked.pid AS blocked_pid,
blocked.query AS blocked_query,
blocking.pid AS blocking_pid,
blocking.query AS blocking_query
FROM pg_stat_activity AS blocked
JOIN LATERAL unnest(pg_blocking_pids(blocked.pid)) AS b(pid) ON true
JOIN pg_stat_activity AS blocking ON blocking.pid = b.pid
WHERE cardinality(pg_blocking_pids(blocked.pid)) > 0;Locks that are still waiting
Every lock a backend has requested but not yet been granted.
SELECT l.pid,
l.locktype,
l.mode,
l.granted,
COALESCE(c.relname, l.transactionid::text) AS object
FROM pg_locks l
LEFT JOIN pg_class c ON c.oid = l.relation
WHERE NOT l.granted
ORDER BY l.pid;Why it happens
What PostgreSQL is telling you
The mechanism behind the error, grounded in the official manual — not paraphrased.
PostgreSQL 16 Documentation — PREPARE
Prepared statements can take parameters: values that are substituted into the statement when it is executed. When creating the prepared statement, refer to parameters by position, using $1, $2, etc.Read the full section on postgresql.org →
The unbound parameter reference
$1 only has meaning inside a prepared statement, where a value gets substituted in at EXECUTE time. Typed as a bare, ordinary query, there's no value anywhere for PostgreSQL to substitute, so it rejects the reference outright.Confirming the session still works
The rejected query didn't affect the session — the next statement ran normally.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.
-- No table needed: the failure happens purely at the parse stage.
SELECT 'no schema required' AS setup_note;SELECT $1;SELECT 1 AS session_still_alive;What PostgreSQL actually returned
setup_note
--------------------
no schema required
(1 row)ERROR: there is no parameter $1
LINE 1: SELECT $1;
^ session_still_alive
----------------------
1
(1 row)A subtler mistake was tested directly: declaring fewer parameter types in PREPARE than the number of $n placeholders actually used in the query body.
PREPARE a statement with one declared type but two $n references, then EXECUTE it with only one argument.
Without this
Above: referencing $1 with no PREPARE context at all is rejected with SQLSTATE 42P02.
With this, tested
Below: PREPARE itself does not catch a parameter-count mismatch — a later EXECUTE call fails instead, with a completely different SQLSTATE.
What Pro unlocks here
- The exact prevention SQL — copy-paste ready
- Raw psql output captured from the Docker lab
- A senior-DBA action list to take it further
- Live monitoring queries to catch it in production
- The deeper audit: fix-that-fails counterexample, GUC before/after, server-log evidence
Related & next steps
Follow the thread
Everything this error touches — jump straight to the sibling error, term, runbook, or parameter.
Verification
- Last verified
- 2026-07-16 (Docker lab, PostgreSQL 16.14)
- Reviewed by
- Verified against PostgreSQL 16.14 in an isolated lab environment
- Audit status
- reviewed