To join an additional table, click + Join table. This allows you to access variables from additional tables in your project, and specify conditions on which to join these tables to your source table.
Once you select a table in your transform, it will be connected to this node by a thin path and its variables will become available throughout this transform.
You'll specify additional join parameters (including the variables on which to join), as well as other transform parameters described above using the node detail view to the right side of the page.
For example, to join records, by provider_id, from the source t0 Medicare Outpatient Charges table with records from the t1 Medicare Inpatient Charges table, we create a comparison that joins records when table's provider_ids are equal.
When you join a new table t1, the variables in that table will be available to keep in the output table or discard using the variable selector interface, prefixed with a t1tag. You can also access these variables when filtering rows, creating new variables, etc.
To specify more complicated join criteria, you can choose to + Join on additional variable to compare variable or literal parameters using additional comparison operators.