Grokking Streaming Systems

8 Join operations

In this chapter

• correlating different types of events in real time
• when to use inner and outer joins
• applying windowed joins

“An SQL query goes into a bar, walks up to two tables, and asks, can I join you?”

—Anonymous

If you have ever used any SQL (structured query language) database, most likely you have used, or at least learned about, the join clause. In the streaming world, the join operation may not be as essential as it is in the database world, but it is still a very useful concept. In this chapter, we are going to learn how join works in a streaming context. We will use the join clause in databases to introduce the calculation and then talk about the details in streaming systems. If you are familiar with the clause, ...