PostgreSQL raises error 42939 (reserved_name) when you try to create, alter, or rename an object using a name that begins with a system-reserved prefix such as pg_, information_schema, or pg_toast.
PostgreSQL Error 42939: reserved_name occurs when an object name starts with a protected prefix like pg_. Rename the table, schema, or column to a non-reserved identifier to resolve the error.
PostgreSQL Error 42939: reserved_name
Error 42939 appears when PostgreSQL detects an identifier that collides with names reserved for system catalogs or temporary objects. The server blocks the statement to protect internal metadata.
The error is flagged by the parser before execution.
It applies to CREATE, ALTER, RENAME, and DROP commands involving schemas, tables, columns, indexes, constraints, or functions that start with pg_ or other reserved prefixes.
Using identifiers that begin with pg_, information_schema, pg_toast, pg_temp_, or pg_catalog triggers the problem.
PostgreSQL treats these prefixes as off-limits for user objects.
Automated tools that prepend pg_ to names, sloppy copy-paste from examples, or renaming production objects without validation frequently introduce the conflict.
Rename the object to drop the reserved prefix. You can ALTER or DROP and recreate the object with a valid name.
Quoting the identifier does not bypass the rule.
If a third-party migration script generates the name, override its naming template or add a custom prefix that does not clash with system namespaces.
Creating a schema called pg_data fails. Rename it to app_data.
Renaming a user table to pg_users in a refactor fails.
Choose users_pg instead or store the prefix at the end.
Establish a naming convention that reserves pg_, information_schema, and pg_toast exclusively for the database engine.
Integrate linting in CI pipelines. Galaxy’s AI copilot flags invalid prefixes in real time, preventing errors before code reaches production.
Error 42P07 (duplicate_table) arises when a conflicting table already exists.
Resolve by renaming or dropping the duplicate.
Error 42P01 (undefined_table) surfaces when a referenced table is missing. Check search_path and object existence.
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No. Even with double quotes, PostgreSQL blocks reserved prefixes. You must choose a different identifier.
The check is hard-coded for safety. Modifying PostgreSQL source and recompiling is the only way, which is strongly discouraged.
pg_, pg_temp_, pg_toast_, pg_catalog_, and information_schema are the main protected prefixes.
Temporary tables you create must also avoid reserved prefixes. PostgreSQL internally uses pg_temp_ for its own temp objects.
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