Joins

A transform that performs equijoins across two schema PCollections.

This transform allows joins between two input PCollections simply by specifying the fields to join on. The resulting PCollection<Row> will have two fields named “lhs” and “rhs” respectively, each with the schema of the corresponding input PCollection.

For example, the following demonstrates joining two PCollections using a natural join on the “user” and “country” fields, where both the left-hand and the right-hand PCollections have fields with these names.

PCollection<Row> joined = input1.apply(Join.innerJoin(input2).using("user", "country"));

If the right-hand PCollection contains fields with different names to join against, you can specify them as follows:

PCollection<Row> joined = input1.apply(Join.innerJoin(input2)
       .on(FieldsEqual.left("user", "country").right("otherUser", "otherCountry")));

Supported methods

• Full outer join
• Left outer join
• Right outer join
• Inner join
• Left inner join
• Right inner join

Playground exercise

In the playground window you can find examples of using the Join. By running this example, you will see user statistics in certain games.

You can use other joins simply by changing the function name:

.apply(Join.fullOuterJoin(gameInfo).using("userId"));