not_null_violation null value in column “…” violates not-null constraint — 23502

Symptoms

An INSERT or UPDATE left a NOT NULL column without a value (or set it to NULL). PostgreSQL rejects the row with SQLSTATE 23502 (not_null_violation).

• The DETAIL shows the failing row, with NULL in the offending column.
• Common when a column has no default and the app omits it.
• Also appears when adding a NOT NULL column to a table with existing rows.

What the server log shows

ERROR:  null value in column "email" of relation "users" violates not-null constraint
DETAIL:  Failing row contains (17, null, …).

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.”

Before storing a row, PostgreSQL verifies every NOT NULL column holds a non-null value. A missing value with no default, or an explicit NULL, fails the check and the row is rejected with 23502.

Common causes

• The application did not supply a required column and there is no default.
• Inserting NULL explicitly into a required column.
• Adding a NOT NULL column without a default to a populated table.

How to fix it

1. Provide a value for the column in the INSERT/UPDATE.
2. Give the column a sensible DEFAULT if appropriate.
3. When adding a NOT NULL column to existing data, add it with a default or backfill first, then set NOT NULL.

Related & next steps

• SQLSTATE 23502 — Not Null Violation (full reference)
• Message: new row violates check constraint
• Glossary: Not-null constraint

Reference: PostgreSQL 18 Section 5.5 “Constraints”.