null value in column “…” of relation “…” violates not-null constraint

Symptoms

A row being inserted or updated left a NOT NULL column empty. PostgreSQL names the column and table and shows the failing row in the DETAIL line.

• The write is rejected and the transaction rolls back with SQLSTATE 23502.
• The DETAIL line shows the failing row, with null in the offending column.
• Usually a column was omitted (with no default) or set to NULL explicitly.

What the server log shows

ERROR:  null value in column "email" of relation "users" violates not-null constraint
DETAIL:  Failing row contains (42, null, 2026-01-01).
STATEMENT:  INSERT INTO users (id, created_at) VALUES (42, now());

Why PostgreSQL raises this — what the manual says

Section 5.5.2 Not-Null Constraints:

“A not-null constraint simply specifies that a column must not assume the null value.”

When a write produces a row whose NOT NULL column holds NULL — because the column was omitted and has no default, or was set to NULL explicitly — the constraint fails with 23502 and the whole statement rolls back.

Common causes

• Omitting a required column that has no DEFAULT.
• Inserting an explicit NULL into a required column.
• An application sending an empty/missing field as NULL.
• An UPDATE that nulls out a required column.

How to fix it

1. Provide a value for the column in every insert/update.
2. Add a sensible DEFAULT: ALTER TABLE users ALTER COLUMN created_at SET DEFAULT now();.
3. Fix the application mapping so the field is always populated.
4. If the column should allow blanks, drop the constraint: ALTER TABLE users ALTER COLUMN email DROP NOT NULL;.

Related & next steps

• SQLSTATE 23502 — Not-Null Violation (full reference)
• Message: new row violates check constraint
• Message: duplicate key value violates unique constraint

Reference: PostgreSQL 18 Section 5.4.2 “Not-Null Constraints”.