mysql dump best practices for development
mysqldump --opt --where="1 limit 10" database


It's an SQL injection:
The --where option is basically appended to a query of the form SELECT * from table WHERE , so in this case you get SELECT * from table WHERE 1 limit 10. Without the 1, you would have an invalid query. Specifying 1 for a where clause (since 1 is always true) simply selects all records.

Source: Limiting the number of records from mysqldump?