Using SQLDeveloper with MySQL databases, you may see “Query execution was interrupted” errors.
To use SQLDeveloper to talk to MySQL databases, you need to use a specific version of the MySQL java driver. This is due to a bug in the driver. It is not an issue with SQLDeveloper.
Download mysql-connector-java-5.1.18.zip (or tar.gz) from MySQL and extract the *-bin.jar file from the root of the archive (or use this local link).
Put the *-bin-jar file wherever you like.