U148: Object already exists

Example Postgres Log Output:

ERROR:  relation "mytable" already exists
STATEMENT:  CREATE TABLE mytable (id int);

ERROR:  column "created_at" of relation "mytable" already exists
STATEMENT:  ALTER TABLE mytable ADD COLUMN created_at timestamptz;

ERROR:  type "status" already exists

Explanation:

A CREATE or ALTER command tried to create an object whose name is already taken. This covers every object kind since the cause and the fix are the same regardless of kind.

Note that “already exists” is judged by name within the relevant namespace, not by definition. CREATE TABLE mytable fails if any relation named mytable exists in the schema, including a view, sequence, index or foreign table. Roles and databases are cluster-wide, so those conflicts can come from outside the current database entirely.

Recommended Action:

The most common source of this event is a migration being applied twice: a retried deploy, two application instances racing to run migrations at boot, or a migration that was partially applied and then re-run after an error.

For idempotent commands, IF NOT EXISTS variants can avoid this error, but they only match on name, so they cannot ensure a known-good state.

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