SQLSTATE 42803Severity lowLab verified

Incident brief

Column must appear in GROUP BY

A non-aggregated column in the SELECT list of a grouped query must appear in GROUP BY or be wrapped in an aggregate; otherwise PostgreSQL raises this grouping error.

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: Column must appear in GROUP BY
What triggers it: Write a GROUP BY query that selects a column which is neither grouped nor aggregated.
The fix: Wrap the column in an aggregate (SUM, MAX, ...).
Proof: Reproduced on PostgreSQL 18.4 → A single query reproduces SQLSTATE 42803; the ungrouped column is rejected and the LINE points at it.

The fix

What to do right now

The immediate, application-level response to this error.

Wrap the column in an aggregate (SUM, MAX, ...).
Or add the column to the GROUP BY clause if you meant to group by it.

Fix — SQL

-- Aggregate the column (or add it to GROUP BY).
SELECT customer_id, sum(amount) FROM sales_line GROUP BY customer_id;

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.

1Write a GROUP BY query that selects a column which is neither grouped nor aggregated.
2PostgreSQL checks that every output column is determined by the grouping.
3The ungrouped, unaggregated column aborts the statement with SQLSTATE 42803.

A per-customer total selected the raw amount alongside GROUP BY customer_id, and the query would not run until amount was aggregated.

Schema setup

CREATE TABLE sales_line(customer_id int, amount numeric);
INSERT INTO sales_line VALUES (1, 20),(1, 30);

Selecting an ungrouped, unaggregated column

SELECT customer_id, amount FROM sales_line GROUP BY customer_id;

The session continues normally

SELECT 'ok' AS session_after_error;

What PostgreSQL actually returned

Schema setup output

CREATE TABLE
INSERT 0 2

Selecting an ungrouped, unaggregated column output

ERROR:  column "sales_line.amount" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT customer_id, amount FROM sales_line GROUP BY customer...
                            ^

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