What we performed is an Inner join of the two tables. There are also other joins, such as Left, Right, and Full Outer, offered in Tableau. They're generally available to switch between, in the Join window.
Using an inner join was appropriate in our case, because all of the rows in both tables could be matched—thanks to a unique key field. The inner joins produce tables with cases that have been matched in both tables.
The Left join keeps all of the values from the left tables, while using only the cases from the right table that have a match in the left table, as shown in the following screenshot:
The Right join works on the same principle, but keeping all of the values from the right table, as shown in the following screenshot:
Finally, a Full Outer join keeps all of the cases from both tables, regardless of whether they have a match in the other table or not. Null values will be placed in cases where a match isn't found:
As of the 2018.2 release, Tableau also offers another kind of joins—Spatial joins. They allow you to join points and polygons from spatial tables on the basis of their location. This is achieved through a new joining predicate known as intersect, which matches the location of points from one table to polygons in another table, joining data when a point lies within a polygon.