duplicate JSON object key value: “…”

SQLSTATE 22030 condition duplicate_json_object_key_value class 22 — Data Exception severity ERROR

Reproduced & verified on PostgreSQL 14.23, 15.18, 16.14, 17.10 and 18.4 — identical message on every version.

Last reviewed 30 May 2025 · Reproduced live with the SQL on this page.

Symptoms

A JSON value being parsed into jsonb (with duplicate-key checking) contained the same object key twice. PostgreSQL raises SQLSTATE 22030 (duplicate_json_object_key_value).

A JSON object has a repeated key.
Raised when strict duplicate-key checking is in effect.
Common with hand-built or merged JSON.

What the server log shows

ERROR:  duplicate JSON object key value: "id"

Why PostgreSQL raises this — what the manual says

Section 9.16 JSON Functions and Operators:

“If WITH UNIQUE is specified, the expression must not contain any duplicate object keys.”

While jsonb normally keeps only the last value for a duplicate key, builder functions invoked with key-uniqueness checking reject duplicates outright. Encountering a repeated key under that check yields 22030.

Common causes

A JSON object literal with the same key listed twice.
Merging objects that share keys with unique-key checking on.
A JSON-building function called with duplicate keys.

How to fix it

Remove the duplicate key so each key appears once.
If last-wins behaviour is acceptable, cast to jsonb without unique-key checking.
De-duplicate keys before building the JSON object.

Related & next steps

Reference: PostgreSQL 18 Section 9.16 “JSON Functions”.