PostgreSQL Error 42P01: Undefined table

Identify: does your log match?

ERROR:  relation "users" does not exist
LINE 1: SELECT * FROM users;
                      ^

1. High

   Migrations not applied to this database

   The code was deployed before the migration that creates the table ran. Common when CI points at a fresh database or a different branch database.

2. Medium

   Table lives in another schema

   Postgres resolves unqualified names through search_path, which defaults to "$user", public. A table in schema app is invisible to SELECT * FROM users.

3. Medium

   Case-sensitive quoted identifier

   A table created as "Users" (quoted) keeps its capital letter. Unquoted users is folded to lowercase and does not match.

Fix

-- table was created in schema "app"
SELECT id, email FROM users;

SELECT id, email FROM app.users;

-- or make it the default for this role
ALTER ROLE api_user SET search_path = app, public;

Verify: reproduce it on purpose

$ psql -c "SELECT * FROM missing_table;"

Prevent

• Run migrations as a release step in CI, not by hand.
• Avoid quoted mixed-case identifiers; use snake_case.
• Pin search_path per role instead of per connection string.