To cancel a query, both Interactive Reporting and the database must communicate properly for reasons other than running a query.
To cancel a query, press and hold Alt+End until the query is cancelled.
The Interactive Reporting database connection file used to connect to the database must use an Asynchronous API. This is the default configuration, but it can be turned off on some databases. If the Asynchronous API is disabled, the database cannot detect a new request until the query has finished processing.
The database must pause every so often even when processing a query. As a default configuration, many databases are not set up to pause, which could result in the database being too busy to hear the cancel request until the query has finished processing.