BigData / Tableau Interview Questions
What are the types of joins supported in Tableau?
When connecting multiple tables from the same data source, Tableau lets you join them using standard relational join types, configured visually in the data source pane.
| Inner Join | Left Join | Right Join | Full Outer Join |
| Only matching rows from both tables. | All rows from the left table, matched rows from the right. | All rows from the right table, matched rows from the left. | All rows from both tables, matched where possible. |
Orders (left table) LEFT JOIN Customers (right table) ON Orders.customer_id = Customers.customer_id -- keeps every order, even ones missing a matching customer record
Tableau shows a visual Venn-diagram-style icon for each join type in the data source pane, making it easy to pick the right one without writing SQL by hand. Choosing the wrong join type is a common source of row duplication or missing data — for example, an inner join silently drops orders that don't have a matching customer, which can understate totals if not caught.
Which join type keeps only rows that match in both tables?
What can happen if the wrong join type causes unmatched rows to be dropped silently?
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