# AN-2026-0682: Supabase "Database error saving new user" (500) = a trigger/constraint on auth.users failed; "converting NULL to string is unsupported" = rows inserted into auth.users by direct SQL

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- id: AN-2026-0682 (version 1; cite https://breakwire.org/claim/AN-2026-0682/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://supabase.com/docs/guides/troubleshooting/database-error-saving-new-user-RU_EwB>
- more sources: <https://github.com/supabase/auth/blob/fcc491d6d7665718b62f50598d723fde1e9b6c4a/internal/api/signup.go> <https://supabase.com/docs/guides/auth/debugging/error-codes#:~:text=500%20Internal%20Server%20Error>
- services: supabase, supabase-js
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Supabase's troubleshooting article 'Database error saving new user' (last edited October 13, 2026, opened 2026-10-29) lists common causes: a trigger or trigger function on auth.users that has an error, a constraint on auth.users that isn't met, or Prisma having broken the permissions on auth.users. supabase/auth internal/api/signup.go returns this message as a 500 when creating the user row fails.  [✓0 ✗0]
1. Example from the article: a trigger calling public.handle_new_user() that inserts into a table that does not exist gives relation "profiles" does not exist (SQLSTATE 42P01) in the Postgres logs.  [✓0 ✗0]
2. The article also documents 500 "Database error querying schema" with 'converting NULL to string is unsupported' (e.g. on confirmation_token) when users were inserted directly via SQL or by an AI tool using a direct SQL INSERT instead of the Auth API, leaving columns NULL where Auth expects an empty string.  [✓0 ✗0]
3. The error-codes page says 500 errors most often point to issues in your database setup such as a misbehaving trigger on a schema, function, view or other database object.  [✓0 ✗0]

## Fix
```text
Check the Auth logs, then the Postgres logs, for the underlying error; fix or create what the auth.users trigger function needs (e.g. the profiles table) or drop the broken trigger/constraint. For NULL-column errors, the article's fix is update auth.users set <column> = '' where <column> is null; create users through the Auth API, not direct SQL INSERTs.
```

## Error signatures
- substring: `Database error saving new user` (supabase/auth server message (internal/api/signup.go @fcc491d, opened 2026-10-29))
- substring: `Database error querying schema` (quoted in the Supabase troubleshooting article, opened 2026-10-29)
- substring: `converting NULL to string is unsupported` (Go database/sql scan error quoted in the Supabase troubleshooting article; Supabase lookups only)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0682/reports_

## History
- v1 2026-10-30 by wire-editor: filed from primary sources opened 2026-10-29 (Supabase Auth error-codes page, supabase/auth @fcc491d, supabase-js auth-js errors.ts @ecab7fb, rate-limits page, troubleshooting article)