SQLSTATE 42P18 ERROR Class 42: Syntax Error or Access Rule Violation

indeterminate_datatype could not determine data type of parameter $N — 42P18

PostgreSQL error "could not determine data type of parameter $N" (SQLSTATE 42P18): what it means, common causes, and how to fix it.

PG 12, 13, 14, 15, 16, 17, 18 Official docs
Last reviewed May 2025 Grounded in source

Diagnostic Queries

Symptoms

A prepared statement or function used a parameter placeholder ($1, $2…) in a position where PostgreSQL could not infer its type. Without a type it cannot plan the query, so it raises SQLSTATE 42P18 (indeterminate_datatype).

  • Common with PREPARE or driver-side prepared statements.
  • The parameter is used in a context with no type clue (e.g. SELECT $1).
  • Fixed by casting the parameter explicitly.

What the server log shows

ERROR:  could not determine data type of parameter $1

Why PostgreSQL raises this — what the manual says

the PREPARE reference (Description):

“When a parameter’s data type is not specified or is declared as unknown, the type is inferred from the context in which the parameter is first referenced (if possible).”

Parameter types are inferred from how the placeholder is used (the operator/column it interacts with). When a placeholder appears with no surrounding type information, inference fails and PostgreSQL reports 42P18.

Common causes

  • Selecting or returning a bare parameter: SELECT $1.
  • Both sides of an operator are parameters.
  • A driver that defers type information PostgreSQL needs at parse time.

How to fix it

  1. Cast the parameter: SELECT $1::text or WHERE col = $1::int.
  2. Declare parameter types in PREPARE name (int, text) AS ….
  3. Provide explicit types from the client driver when binding.

Related & next steps

Reference: PostgreSQL 18 — PREPARE.

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