[BUG] Claude Code deleted 24,000+ database rows with a buggy SQL script and autovacuum prevented recovery

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code wrote and executed a SQL script to clean job titles in a PostgreSQL
table (manager_roles, ~24,475 rows representing 3 days of web scraping).

The script used PostgreSQL's regexp_match() with capture groups in the regex
pattern. Because capture groups were present, regexp_match() returned the
captured subgroup content instead of the full match — causing it to return NULL
for nearly every row. The script then deleted _all rows where the extracted title
was NULL, wiping 24,472 of 24,475 rows._

The transaction committed before I noticed. I immediately disabled autovacuum
on the table and attempted recovery with pg_dirtyread, but autovacuum had
already run (timestamp: 2026-05-06 15:06:12 UTC) and cleaned the dead tuples
before the extension could be installed.

Impact: 24,472 rows permanently deleted. ~3 days of scraping work lost. I feel like I should be compensated on credits for this MAJOR loss.

What Should Happen?

1. Tested the regex on a small SELECT before writing a DELETE
2. Shown a row count and asked for confirmation before committing
3. Wrapped the script in a transaction with an explicit ROLLBACK safety check

Error Messages/Logs

Steps to Reproduce

1. Have a PostgreSQL table with a numeric(3,2) column and ~24,000 rows

1. Ask Claude Code to clean a text column using regex extraction

1. Claude writes and executes the following SQL script without testing first:

ALTER TABLE manager_roles ADD COLUMN IF NOT EXISTS _clean_title TEXT;

UPDATE manager_roles
SET _clean_title = (regexp_match(job_title,
'Executive Vice President and (Chief Executive Officer|CEO)'
'|Chief Executive Officer'
'|CEO|CFO|...',
'i'
))[1];

DELETE FROM manager_roles WHERE _clean_title IS NULL;

-- (followed by dedup DELETE, UPDATE, DROP COLUMN, COMMIT)

1. Because the regex pattern contains capture groups e.g. (Chief Executive

Officer|CEO), PostgreSQL's regexp_match() returns the captured subgroup
content rather than the full match — returning NULL for nearly every row

1. DELETE FROM manager_roles WHERE _clean_title IS NULL wipes 24,472 of

24,475 rows

1. COMMIT runs. Transaction is permanent.

1. Claude attempts pg_dirtyread recovery but autovacuum had already run

and cleaned dead tuples before the extension could be installed.

1. Data is permanently lost.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Sonnet 4.6

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_