Joining is a method for combining related data on a common key. In Tableau, when we work with vast data sets, it is natural that data sets will have multiple tables with different data fields. This means that data does not reside on a single table instead, there are different tables. However, some tables might have common fields. We can join such tables by means of columns that are common or related. Such related fields or identifiers used to form joins are known as Key fields or records.
Thus, related tables are joined or combined from the same or different sources to form a single virtual table which is an extended table having added columns from different tables. It is convenient for the users to use this joined table in data analysis works.
Types of Joins in Tableau