Apama 10.3 | Apama Documentation | Developing Apama Applications | Developing Apama Applications in EPL | Working with Streams and Stream Queries | Defining stream queries | Joining two streams
Joining two streams
Defining cross-joins with two from clauses
Defining equi-joins with the join clause
When a stream query operates over two input streams, it is referred to as a join operation. There are two forms of join operation available in EPL:
*A cross-join joins every event from one stream's window with every event in the other stream's window.
*An equi-join joins events only when they have matching keys.
Each form takes two input streams and produces a single output stream of combined items.
Join operations, particularly cross-joins, can create many more output events than input events, not just the same or fewer.

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