P0004ERRORTier 2 — Caution✅ HIGH confidence

assert_failure

Category: PL/pgSQL ErrorVersions: PostgreSQL 9.5+

What this means

A PL/pgSQL ASSERT statement evaluated its condition as false, causing the function to abort. Used for invariant checking and developer assertions in PL/pgSQL code.

Why it happens

1ASSERT condition evaluated to false or NULL
2Invariant assumed by the developer is violated by actual data or state
3ASSERT used as a debugging tool and left in production code with an edge case not anticipated

How to reproduce

PL/pgSQL function or DO block containing an ASSERT statement whose condition fails

trigger — this will ERROR

DO $
DECLARE
  total int;
BEGIN
  SELECT count(*) INTO total FROM orders;
  ASSERT total > 0, 'orders table must not be empty';
END;
$;

ERROR: P0004: orders table must not be empty

Fix 1: Fix the condition that caused the assertion to fail

The assertion represents a genuine invariant that is now violated

fix

-- Investigate and correct the data or logic that violated the invariant

Why this works

Address the root cause rather than removing or disabling the assertion

Fix 2: Disable assertions for production if they are development-only checks

Assertions are not appropriate for production workloads

fix

-- In postgresql.conf:
-- plpgsql.check_asserts = off

Why this works

Setting plpgsql.check_asserts=off disables all ASSERT checks without removing them from code

What not to do

✗

Do not remove ASSERT statements to fix the error without investigating why the assertion failed

Why it's wrong: Assertions exist to catch bugs; removing them hides the underlying problem

Version notes

9.5ASSERT statement added in PostgreSQL 9.5

Sources

📚 Official docs: https://www.postgresql.org/docs/current/plpgsql-errors-and-messages.html#PLPGSQL-STATEMENTS-ASSERT

🔧 Source ref: https://www.postgresql.org/docs/current/errcodes-appendix.html

Confidence assessment

✅ HIGH confidence

Standard PL/pgSQL error SQLSTATE from official PostgreSQL appendix.