invalid_cursor_definition cannot open … query as cursor — 42P11

Symptoms

A cursor was opened over a query that cannot back a cursor (for example a utility/data-modifying statement). PostgreSQL raises SQLSTATE 42P11 (invalid_cursor_definition).

• The statement type can’t be used as a cursor source.
• Cursors require a query that returns a result set.
• Common with non-SELECT statements.

What the server log shows

ERROR:  cannot open INSERT query as cursor

Why PostgreSQL raises this — what the manual says

As the DECLARE reference (Parameters) explains:

Only a SELECT or VALUES query can back a cursor; a statement that does not return a result set (such as a utility command, or a data-modifying statement without a RETURNING clause) cannot be opened as a cursor.

A cursor iterates over rows produced by a query. Statements that don’t produce a result set (e.g. an INSERT without RETURNING, or utility commands) can’t back a cursor, so PostgreSQL reports 42P11.

Common causes

• Declaring a cursor over an INSERT/UPDATE/DELETE without RETURNING.
• Trying to cursor over a utility/DDL statement.
• Passing the wrong statement to a cursor-opening API.

How to fix it

1. Use a SELECT or VALUES query for the cursor.
2. Add RETURNING if you need rows back from a DML statement (without a cursor).
3. Run utility statements directly rather than via a cursor.

Related & next steps

• SQLSTATE 42P11 — Invalid Cursor Definition (full reference)
• Message: cursor already exists
• Glossary: Cursor

Reference: PostgreSQL 18 — DECLARE.