SQLSTATE 22004Severity lowLab verified

Incident brief

Null value not allowed

A PL/pgSQL variable declared NOT NULL was assigned a null value. PostgreSQL rejected the assignment instead of silently storing null.

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

In 10 seconds

What: Null value not allowed
What triggers it: Declare a PL/pgSQL variable with NOT NULL and a default value.
The fix: Don't assign NULL to a variable declared NOT NULL — check for null first with an IF, or use COALESCE on the source value before assigning.
Proof: Reproduced on PostgreSQL 16.14 → Assigning NULL to a NOT NULL PL/pgSQL variable was rejected with SQLSTATE 22004. The session was unaffected afterward.

The fix

What to do right now

The immediate, application-level response to this error.

Don't assign NULL to a variable declared NOT NULL — check for null first with an IF, or use COALESCE on the source value before assigning.
If null is a valid outcome, drop NOT NULL from the declaration instead of fighting it.

Fix — SQL

DECLARE
  v int NOT NULL := 5;
  incoming int := NULL;
BEGIN
  v := COALESCE(incoming, v); -- keeps v's last good value instead of assigning null
END;

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;

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.

1Declare a PL/pgSQL variable with NOT NULL and a default value.
2Assign it NULL later in the block.
3SQLSTATE 22004 is reported; the block aborts.

One client: a DO block declares a NOT NULL variable, then assigns it NULL.

Schema setup

-- No table needed: this is a pure PL/pgSQL variable rule.
SELECT 'no schema required' AS setup_note;

The rejected assignment

DO $$
DECLARE
  v int NOT NULL := 5;
BEGIN
  v := NULL;
END $$;

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 rejected assignment output

ERROR:  null value cannot be assigned to variable "v" declared NOT NULL
CONTEXT:  PL/pgSQL function inline_code_block line 5 at assignment

Confirming the session still works output

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

Related & next steps

Follow the thread

Everything this error touches — jump straight to the sibling error, term, runbook, or parameter.

Verification

PG 16.14

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