I did this with a DELETE SQL WHERE clause, trying to isolate a set of records, instead selecting all records, in an effort to test a production installation, at 3am (YES) and had to buy 3 db admins lunch the following day because they came in to restore multiple customer tables. The DELETE's were triggered across numerous tables and platforms (AS400 and SQL Server). The walk of shame to tell my director was not my most shining moment. I'd like to go back in time and slap myself just moments before. Running commands on live production data. Silly programmer.
At least with MySQL's tools, thanks to ssh's happiness to work as a pipe, it's very easy to clone a database locally for fucking about when you're trying to do something like this:
ssh remotehost.example.com mysqldump -udbuser proddatabase | mysql -uroot testdatabase
(n.b. the mysqldump options that may lock your production tables during the dump.)
