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Getting Started with Oracle Event Processing 11g by Lloyd Williams, Robin J. Smith, Alexandre Alves

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The structure and semantics of event processing

The structure of CQL queries is very similar to that of SQL. In fact, CQL is based on a subset of SQL99. Let's revisit the simple example from the beginning of the previous section:

SELECT p1 
FROM inputChannel

In this case, the FROM inputChannel clause informs the query that the input events arrive from the source called inputChannel, which happens to be the upstream channel to this CQL processor in the EPN. Further, the SELECT p1 clause states that the query is selecting only the event property p1 for output. The behavior of this query is best described with the following table:

Timet

Input event

Output event

0

{p1 = 1, p2 = "hi"}

{p1 = 1}

In other words, at time t = 0, we receive event ...

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