collation of DEFAULT expression conflicts with RETURNING clause

Symptoms

A statement failed with SQLSTATE 42P21 (collation_mismatch), reported at severity ERROR. This is a Syntax Error or Access Rule Violation condition: PostgreSQL emits the message collation of DEFAULT expression conflicts with RETURNING clause.

• The client receives SQLSTATE 42P21 (collation mismatch).
• The operation is rejected at ERROR level; the statement does not complete.
• The server adds a DETAIL line with specifics (see below).

What the server log shows

ERROR:  collation of DEFAULT expression conflicts with RETURNING clause
DETAIL:  "…" versus "…"

Why PostgreSQL raises this

Class 42 (Syntax Error or Access Rule Violation) is raised at parse/analysis time when a statement is malformed, references an object or column that cannot be resolved, or the role lacks privilege for the action.

As described in PostgreSQL’s Section 4.1 Lexical Structure and Appendix A (PostgreSQL Error Codes), SQLSTATE 42P21 carries the condition name collation_mismatch in class Syntax Error or Access Rule Violation. (Paraphrased — see the linked reference for the exact wording.)

Common causes

• A typo, missing keyword, or misplaced clause in the SQL text.
• An object, column, function, or type name could not be resolved on the search_path.
• Wrong identifier case (unquoted names fold to lower case).
• The role lacks the privilege required for the operation.

How to fix it

1. Read the caret (^) in the log — it points at the offending token.
2. Schema-qualify names or fix search_path; confirm the object exists.
3. Quote mixed-case identifiers exactly as created.
4. Grant the required privilege or connect as a role that has it.

Version applicability

This message text is present in PostgreSQL 17, 18, 19. It was introduced around PostgreSQL 17; earlier releases do not emit this exact text.

Related & next steps

• SQLSTATE 42P21 — Collation Mismatch (full reference)
• PostgreSQL error code index

Reference: PostgreSQL Section 4.1 Lexical Structure.