SQLSTATE 42P06Severity lowLab verified

Incident brief

Duplicate schema

CREATE SCHEMA fails if a schema of that name already exists; IF NOT EXISTS makes the creation idempotent.

Reproduced on PostgreSQL 18.4Verified 2026-07-24 (isolated lab, PostgreSQL 18.4)Reviewed by Verified against PostgreSQL 18.4 in an isolated lab environment

In 10 seconds

What: Duplicate schema
What triggers it: CREATE SCHEMA with a name that already exists.
The fix: Add IF NOT EXISTS to make the CREATE SCHEMA idempotent.
Proof: Reproduced on PostgreSQL 18.4 → A CREATE SCHEMA reproduces SQLSTATE 42P06 on the pre-existing name.

The fix

What to do right now

The immediate, application-level response to this error.

Add IF NOT EXISTS to make the CREATE SCHEMA idempotent.
Or check for the schema first and drop it deliberately before recreating.

Fix — SQL

-- Make the create idempotent with IF NOT EXISTS.
CREATE SCHEMA IF NOT EXISTS reporting;

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.

1CREATE SCHEMA with a name that already exists.
2PostgreSQL finds the schema already present.
3The statement aborts with SQLSTATE 42P06: 'schema already exists'.

A migration re-ran and CREATE SCHEMA collided with the schema it had created on a previous run.

Schema setup

CREATE SCHEMA reporting;

Creating a schema that already exists

CREATE SCHEMA reporting;

The session continues normally

SELECT 'ok' AS session_after_error;

What PostgreSQL actually returned

Schema setup output

CREATE SCHEMA

Creating a schema that already exists output

ERROR:  schema "reporting" already exists

The session continues normally output

 session_after_error 
---------------------
 ok
(1 row)

Related & next steps

Follow the thread

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

Verification

PG 18.4

Last verified: 2026-07-24 (isolated lab, PostgreSQL 18.4)
Reviewed by: Verified against PostgreSQL 18.4 in an isolated lab environment
Audit status: reviewed