How to diagnose and fix the 42939 reserved_name error code in Postgres.

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The 42939 error code in PostgreSQL refers to a RESERVED_NAME error. This means that you’re attempting to use a name for a table, column, or other database object that is reserved by the PostgreSQL system for its own use or is otherwise restricted by the SQL standard.

To diagnose and fix this issue, you should:

  1. Identify the name that is causing the issue.
  2. Check if it is indeed a reserved keyword in PostgreSQL.
  3. Rename the object using a name that is not reserved.

Here are some examples and sample code to explain and cover the possibilities:

Example 1: Table Creation

If you try to create a table with a reserved name, such as user, which is a reserved keyword in SQL:

CREATE TABLE user (
    id serial PRIMARY KEY,
    username text NOT NULL
);

To fix this, you should rename the table to something that is not a reserved keyword:

CREATE TABLE app_user (
    id serial PRIMARY KEY,
    username text NOT NULL
);

Example 2: Column Naming

Similarly, trying to create a column with a reserved name, like select:

CREATE TABLE employee (
    select integer PRIMARY KEY,
    name text NOT NULL
);

You can resolve this by choosing a different column name:

CREATE TABLE employee (
    selection integer PRIMARY KEY,
    name text NOT NULL
);

Example 3: Using Reserved Words as Identifiers

If you absolutely must use a reserved word as an identifier, you can do so by quoting it:

CREATE TABLE "user" (
    "select" integer PRIMARY KEY,
    name text NOT NULL
);

However, this is generally discouraged because it can lead to confusion and is prone to errors in future queries.

General Tips

  • Always consult the PostgreSQL documentation for a list of reserved keywords.
  • Try to use descriptive and unambiguous names for your database objects to avoid such conflicts.
  • If you encounter a RESERVED_NAME error, double-check your naming against the list of reserved keywords and adjust accordingly.

By following these guidelines, you should be able to diagnose and resolve the 42939 reserved name error in PostgreSQL. Remember to always check against the list of reserved keywords when naming your database objects to prevent these kinds of errors.

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