Accomplish most common querying tasks using a set of queries available in the Visual editor: filter, aggregate, join, compute, union, and pattern.
The tools for these six queries are available as objects in
the Palette, in Streams and Windows.
Filter – allows you to filter a stream down to only the events of interest, based on a filter expression. Similar to SQL WHERE clause.
Aggregate – allows you to group events that have common values and compute summary statistics for the group, such as an average. You can also define a window size, based on either time or number of events. Uses the CCL GROUP BY clause, similar to SQL GROUP BY.
Join – allows you to combine records from multiple streams or windows, forming a new record with information from each source. Comparable to a join in SQL, where you specify two or more sources in the FROM clause.
Compute – allows you to create a new event with a different schema, and compute the value to be contained in each column (field) of the new event. Comparable to a projection in SQL, where you use a SELECT statement to specify the column expressions, and FROM to specify a single source.
Union – allows you to combine multiple streams or windows that all share a common schema into a single stream or window. Similar to SQL UNION operator.
Pattern – lets you watch for patterns of events within a single stream or window or across multiple streams and windows. When ESP Server detects an event pattern in a running project, it produces an output event. This uses the CCL MATCHING clause.
| Simple Query | CCL |
|---|---|
| Filter | WHERE clause |
| Aggregate | GROUP BY clause |
| Join | FROM clause, WHERE clause, ON clause |
| Compute | Simple SELECT statement, with column expressions |
| Union | UNION clause |
| Pattern | MATCHING clause |
Simple Queries from CCL Statements
If you create queries in CCL and want them to appear as simple query shapes in
the Visual editor, you must insert a comment immediately preceding the CREATE STREAM, CREATE
WINDOW, or CREATE DELTA STREAM
statement, in the
form:
/**@SIMPLEQUERY=QUERY_TYPE*/where QUERY_TYPE is the shape name in the Visual editor.
For example, this comment causes a CREATE WINDOW statement to map to an Aggregate shape in the Visual editor: /**@SIMPLEQUERY=AGGREGATE*/ .
Without this comment immediately preceding the CREATE WINDOW statement, the Visual editor shows the generic Derived Window shape.
Note: You cannot modify CCL code in the CCL editor and in the Visual editor concurrently.
If the Visual editor is open, then the CCL editor becomes read-only.
CCL Statements from Simple Queries
When you create a simply query from the Palette, the CCL element it creates is based on these rules:
- If the input for the filter object is a stream, the filter object creates a stream. If the source is a window, delta stream, or flex stream, the filter object creates a delta stream.
- All aggregate objects create a window.
- If the input for a compute object is a stream, the compute object creates a stream. If the source is a window, delta stream, or flex stream, the compute object creates a delta stream.
- If a join object takes input only from streams, then the join object creates a stream. If the source is from one or more windows, delta streams, or flex streams, then the join object creates a window. In a stream-window join, the join object creates a stream.
- If the input of a union object is a stream, the union object creates a stream. If the source is a window, delta stream, or flex stream, the union object creates a delta stream.
- All pattern objects create a stream.