The explicit Join
prefix can be preceded by the prefix Outer to specify an outer join. In an outer join, all combinations between
the two tables are generated. The resulting table will thus contain combinations of field values from the raw data tables where the linking field values are represented in one or both tables. The Outer keyword is optional and is the default join type used when a join prefix is not specified.
In this example, the two tables, Table1 and Table2, are merged into a single table labeled Table1. In cases like this, the outer prefix is often used to join several tables into a single table to perform aggregations over the values of a single table.