To automatically join two tables together, put them inside brackets separated by a '+', e.g.:
select * from [gameplays+users]; select * from [gameplays+users+purchases];
Periscope Data will choose join routes based on the tables' primary keys, foreign keys, and common naming conventions.
For example, let's join gameplays to users in order to split gameplays by users.platform:
Click the "SQL" button above the chart to see the join routes Periscope selected: