Query Operation

Event data retrieved from storage via the repository or a view is then executed through the Query Pipeline. This processes the events and creates a grouping, called the Event Set.

Pipelines define how data will be processed, with each step in the pipeline performing a specific action, such as filtering or modifying the data.

In some places within queries a subquery can be included. Subqueries are executed along with the primary query, and may be used to perform additional filtering, data selection, or formatting. For more information on subqueries, see Subqueries.

The context of a query, that is, where in the system the query is executed, is important because it can limit or restrict the number of available operations or functions. For more information on the different contexts available, see Query Context.

Limits within CQL are designed to ensure query performance and prevent a single query from consuming all available cluster resources during execution. Different limits apply at different stages of the query process, and are related to the query operations and statements being executed. See Effects of Limits.

Identifying issues in a query and fixing errors can be complex. Troubleshooting Queries provides some guides and steps to follow to determine the underlying issue and then fix the query.

The best performing queries are generally written by following certain best practice. For more information, see Query Performance.

Ensuring your queries are readable, commented, and formatted can help both with diagnosing issues and also sharing and developing new queries, especially across a dashboard with multiple widgets. See Query Readability and Format for guides on formatting queries effectively.