In this tutorial you will learn how to combine information from different sources.

We will use the same setting as in Simple Query Processing. So you should follow steps 1-4.


One of the most important operators to combine events from different streams is the join operator.

To combine two elements from different streams, two conditions must hold:

  1. The time intervals must overlap
  2. The join predicate must evaluate to true

Create a new PQL based script (join1.qry) with the following  input:

#TRANSCFG Standard
out = JOIN({PREDICATE=' = nexmark:bid.bidder'},nexmark:person, nexmark:bid)

This query add to each bid the person that is bidding.

After starting you should see something like in the following.

WARNING: In this example we use no windows. For Joins this is typically not recommended, as it can lead to memory overflow!

In most cases it is easy to define a window for each input stream.

There are some case, where you can speed up processing or cope with the case where no windows can be defined by using the parameter CARD:

For the example above, each bid has exactly one person. So we can write:

#TRANSCFG Standard
out = JOIN({PREDICATE=' = nexmark:bid.bidder', CARD='ONE_MANY'},nexmark:person, nexmark:bid)

And this lead to the same output.