PostgreSQL error: null value violates not-null constraint

SQLSTATE 23502 (not_null_violation) · Updated July 9, 2026

ERROR:  null value in column "email" of relation "users" violates not-null constraint
DETAIL:  Failing row contains (42, null, Alice, 2026-07-09 10:12:00).

The write would have left a NOT NULL column empty, so PostgreSQL rejected it. The DETAIL line shows the entire failing row, with values in the table's column order — line it up against \d output and you can see exactly what arrived.

What this error means

One mechanism here surprises almost everyone at some point: column defaults apply only when the column is omitted from the INSERT (or explicitly given the DEFAULT keyword). An INSERT that lists the column and passes NULL means NULL — the default does not kick in. ORMs that serialize every mapped field, sending null for unset ones, silently disable your database defaults this way.

Common causes

• INSERT omitting a required column that has no default.
• Explicit NULL from the application (the ORM pattern above) overriding an existing DEFAULT.
• UPDATE setting the column to NULL, directly or via a computation that produced NULL.
• Data loads: in COPY ... CSV, an unquoted empty field is read as NULL (a quoted empty string "" is not).

How to diagnose it

\d users   -- quali colonne sono NOT NULL, quali hanno un DEFAULT

Map the DETAIL row onto the column list to identify the offending field, then find who produced the NULL: application payload, ORM serialization, or the input file. Logging the actual SQL the app sends settles the "but we set a default!" conversations quickly.

How to fix it

• Provide the value, or add a genuine default: ALTER TABLE users ALTER COLUMN created_at SET DEFAULT now();
• ORM sending NULLs → configure it to omit unset columns, or set the default in the model as well as the database.
• CSV loads → control NULL handling explicitly (NULL '' option, or clean the file); load into a staging table when in doubt.
• If NULL is actually legitimate for the business, drop the constraint deliberately: ALTER TABLE users ALTER COLUMN email DROP NOT NULL; — a decision, not a workaround.